The Camberwell Collaborative Depression Study is an investigation of a series of 130 patients (76 female; 54 male) attending the Maudsley Hospital Services with unipolar depression of recent onset (the probands), and of their first-degree relatives. This paper describes the first element of the study, the investigation of the index cases or probands, which was carried out by members of the MRC Social Psychiatry Unit over the period 1982–1985. A description of the methods of the study is followed by an analysis of life events in relation to the symptomatic pattern of the depressive state. An ‘endogenous' group was defined as cases of depression falling within Catego classes D and R, and compared with a ‘neurotic’ group conforming to classes N and A. The hypothesis that the ‘endogenous' group of disorders would be relatively independent of prior life stress was not confirmed. Depressed women were more likely to have experienced life events or difficulties than their male counterparts, and there was some evidence that sex, but not age or social class, influenced the relationship between adversity and the type of depression. Examination of the timing of life events was strongly suggestive of a causal effect, with a pronounced rise in the month before onset. This was not limited to the most severe events. Differences between the ‘endogenous' and ‘neurotic’ groups in the temporal patterning of events before onset are discussed. The findings are interpreted in terms of the literature on the topic.