Negligence cases in the High Court by nature present difficult policy choices and take place against the context of judicial recognition of the nature of Australian society, social values and human behaviour. Judges, inevitably, make assumptions and statements in their judgments about society and social values, the nature of the world, and human and institutional behaviour. This article refers to these statements as social facts. The article analyses the nature of the concept ‘social fact’, discusses the rules of evidence relating to the reception of social facts in the Australian High Court and presents a study of the use of social facts in High Court negligence cases in 2003. The study discusses the frequency of the use of social facts, the nature of social fact statements made, the source of social facts, the use of social scientific evidence and the use of social facts in Cattanach v Melchior. Overall the article argues that there is no coherent method in Australian law for determining reliable social facts and that this results in the adoption of conflicting and potentially inaccurate assumptions in the Australian High Court.