The maxim res ipsa loquitur or ‘the thing speaks for itself’, is a long-standing rule of evidence more commonly utilised in other areas of personal injury law. In a PI setting it has been applied in a wide range of cases including objects falling from buildings, malfunctioning machines, collapsing cranes, and stones in buns.

In clinical negligence, claimant practitioners often bolt-on an assertion that res ipsa loquitur applies when drafting letters of claim or pleadings. This is often seen in cases where negligence appears more likely on the bare facts.

However, there are strict controls on the application of res ipsa loquitur. Three conditions are required to be met (Scott and Bennett v Chemical Construction (GB) Ltd [1971] 3 All ER 822):

  1. The event is one that would ordinarily not occur in the absence of negligence/fault;
  2. The thing causing the damage must have been under the control of the defendant;
  3. There is no evidence as to why or how the accident occurred.

Once those three conditions are met, the court may draw an inference of negligence against the defendant. The burden of proof then shifts to the defendant, who must prove that the accident was not caused by their negligence. Where the defendant cannot discharge that burden, a claimant may succeed in their claim without proving precisely how their injury was caused.


Its use in clinical negligence gained some traction before Bolam and Bolitho. Mahon v Osborne [1939] 1 All ER 535, is an early example of the application of res ipsa loquitur in a case where a surgical swab had been left inside a patient’s body.

In Clarke v Worboys (1952) Times, 18 March, CA, a patient noticed burns on her buttock shortly after surgical excision of a breast tumour. The surgery involved cauterisation. The Court of Appeal held that this was a case where res ipsa loquitur applied. The outcome was not one that would ordinarily occur in the absence of negligence, and the surgical team were unable to explain how the injury was caused.

In Cassidy v Ministry of Health [1951] 2 KB 343, Denning LJ succinctly summarised the maxim’s application to clinical negligence cases: “I went into hospital to be cured of two stiff fingers. I have come out with four stiff fingers and my hand is useless. That should not happen if due care had been used. Explain it if you can.”


Post-Bolam, its use waned. In Delaney v Southmead Health Authority [1995] 6 Med LR 355, Stuart-Smith LJ said that he was doubtful whether res ipsa loquitur would be of assistance in medical negligence cases, where unexpected results often occur in the absence of negligence.

Glass v Cambridge Health Authority [1995] 6 Med LR 91 is a rare example of res ipsa loquitur surviving Delaney. Here, an otherwise fit and healthy 35 year old underwent an exploratory laparotomy, during which the oximeter alarm went off. It was considered to be a false alarm and switched off. Later, the patient went into cardiac arrest during surgery and suffered brain damage. The Court of Appeal held that res ipsa loquitur applied, and that the defendant had not discharged the reversed burden.

Further doubt of the application of res ipsa loquitur in clinical negligence cases was expressed by Hobhouse LJ in Ratcliffe v Plymouth and Torbay Health Authrity [1998], where it was observed:

“Res ipsa loquitur is not a principle of law and it does not relate to or raise any presumption. It is merely a guide to help identify when a prima facie case is being made out. Where expert and factual evidence is being called on both sides at trial its usefulness will normally have been long since exhausted.”

However, in the same Court of Appeal case, Brooke LJ (with whom both Hobhouse LJ and Sir John Vinelott agreed) reviewed a number of cases concerning the application of res ipsa loquitur in clinical negligence and stated the following principles:

“(1) In its purest form the maxim applies where the plaintiff relies on the res (the thing itself) to raise the inference of negligence, which is supported by ordinary human experience, with no need for expert evidence.

(2) In principle, the maxim can be applied in that form in simple situations in the medical negligence field (surgeon cuts off right foot instead of left; swab left in operation site; patient wakes up in the course of surgical operation despite general anaesthetic).

(3) In practice, in contested medical negligence cases the evidence of the plaintiff, which establishes the res, is likely to be buttressed by expert evidence to the effect that the matter complained of does not ordinarily occur in the absence of negligence.

(4) The position may then be reached at the close of the plaintiff's case that the judge would be entitled to infer negligence on the defendant's part unless the defendant adduces evidence which discharges this inference.

(5) This evidence may be to the effect that there is a plausible explanation of what may have happened which does not connote any negligence on the defendant's part. The explanation must be a plausible one and not a theoretically or remotely possible one, but the defendant certainly does not have to prove that his explanation is more likely to be correct than any other. If the plaintiff has no other evidence of negligence to rely on, his claim will then fail.

(6) Alternatively, the defendant's evidence may satisfy the judge on the balance of probabilities that he did exercise proper care. If the untoward outcome is extremely rare, or is impossible to explain in the light of the current state of medical knowledge, the judge will be bound to exercise great care in evaluating the evidence before making such a finding, but if he does so, the prima facie inference of negligence is rebutted and the plaintiff's claim will fail. The reason why the courts are willing to adopt this approach, particularly in very complex cases, is to be found in the judgments of Stuart-Smith and Dillon L.JJ. in Delaney [see P181 supra].

(7) It follows from all this that although in very simple situations the res may speak for itself at the end of the lay evidence adduced on behalf of the plaintiff, in practice the inference is then buttressed by expert evidence adduced on his behalf, and if the defendant were to call no evidence, the judge would be deciding the case on inferences he was entitled to draw from the whole of the evidence (including the expert evidence), and not on the application of the maxim in its purest form.”

Unlike Hobhouse LJ, Brooke LJ considered that expert evidence would serve to strengthen a res ipsa loquitur argument where the expert confirmed that the result would not ordinarily occur in the absence of negligence. Brooke LJ also explained that any non-negligent possible explanation would have to be greater than merely theoretically or remotely possible.

Modern Compromise?

In more recent times there have been a number of cases in which res ipsa loquitur or similar principles were held to apply.

Thomas v Curley [2013] EWCA Civ 117 concerned a common bile duct injury sustained during laparoscopic cholecystectomy. In what was described as ‘an uncomplicated operation’, injury was caused in an area other than that where the operation took place. The Court of Appeal held that this fact “called for an explanation as to how that might have occurred in the absence of negligence.” Despite this feature, the Court of Appeal went on to say that this approach “has nothing to do with the reversal of the burden of proof and nothing to do with res ipsa loquitur.” It was held that negligence had been proved directly by the claimant.

A similar approach was taken by Jackson LJ in O’Connor v The Pennine Acute Hospitals NHS Trust [2015] EWCA Civ 1244. Here, it was held that whilst the defendant had not proffered any plausible explanation for how an injury could occur in the absence of negligence, this did not reverse the burden of proof, or invoke res ipsa loquitur. Jackson LJ did state that the defendant’s failure to provide an explanation was a matter that the trial judge was entitled to take into account, which supported the finding of negligence against the defendant.

Jackson LJ did not go so far to say that the circumstances called for an explanation by the defendant. However, his approach is virtually one of drawing an inference of negligence because of the absence of explanation by the defendant.

It is difficult, if not impossible, to distinguish Court of Appeal’s ‘calling for an explanation’ approach in Thomas, with Denning’s approach in Cassidy. Requiring the defendant to explain anything must at least amount to a modification of the ordinary burden of proof.

Similarly, Jackson LJ’s ‘taking into account’ of the lack of plausible explanation by the defendant, is at least in part an inference of negligence.

Surgical cases can be more evidentially challenging for claimants. They will usually not have witnessed events because they have been under general anaesthetic. Often the surgeons are unaware of complications until after surgery. Where an unexpected surgical outcome occurs in these circumstances, claimants will often find it useful to advance an alternative case on a res ipsa loquitur footing.

Alternatively, an unexpected outcome may be said to call for an explanation (Thomas). Or, if the defendant fails to put forward a more than theoretically possible explanation, this may itself be a factor which goes to prove negligence, or allows negligence to be inferred (O’Connor).


A final note on pleading res ipsa loquitur. The prevailing view is that it is not necessary to plead the doctrine itself, however, the claimant must allege and prove the facts that allow the inference to be drawn (Scott and Bennett v Chemical Construction (GB) Ltd [1971] 3 All ER 822).

It is likely to assist claimants hoping for a judge to adopt a Thomas or O’Connor approach, to clearly set out that the facts that require a more than theoretically possible explanation by the defendant.