In 2002, Paul Cotton died of lung cancer. Cotton had smoked around 15 to 20 cigarettes a day for over 26 years before he was diagnosed with lung cancer. He had also been exposed to respirable asbestos fibres in the course of his employment with the State of South Australia (the State) and then with Millennium Inorganic Chemicals Ltd (Millennium). His exposure to asbestos when working for the State resulted from working with asbestos cement pipes manufactured by Amaca Pty Ltd (formerly James Hardie & Coy Pty Ltd) (Amaca).

It is well established that both smoking and breathing respirable asbestos can cause lung cancer, however there was no medical evidence to establish what had caused Cotton's lung cancer. Despite this, Cotton pursued actions in negligence against the State, Millennium and Amaca in the Supreme Court of Western Australia. The trial judge found that breaches of the duties owed by all three defendants to Cotton had resulted in him being exposed to asbestos fibres, which had in turn caused, or materially contributed to, his lung cancer. This decision was upheld by the W.A. Court of Appeal.

On appeal to the High Court the big question was causation, namely whether Cotton's exposure to asbestos had caused or materially contributed to his lung cancer. The case for Cotton relied on a House of Lords decision in which it was stated that any contribution which is not minimal must be material. Cotton argued that the combined effect of smoking and asbestos exposure is 'multiplicative', in that it significantly increases the risk of developing lung cancer. It was argued that the contribution of asbestos exposure was not minimal and must therefore have materially contributed to Cotton's condition.

However the High Court distinguished the House of Lords decision on the basis that the cause of the plaintiff's condition had been known in that case (exposure to silica dust) and in that case the question was whether a particular period of exposure had materially contributed to the resultant disease. In Cotton's case, the question was whether one substance that could have caused his injury did cause his injury. Based on the statistical evidence, the High Court held that the evidence established only that exposure to asbestos may have been a cause of Cotton's lung cancer, not that it was a probable cause. So the claim failed.

Amaca Pty Ltd v Ellis