BACKGROUND: Depression affects outcome following myocardial infarction but the risk factors for such depression have been little studied. This study considered whether the causes of depression occurring before and after myocardial infarction were similar to those of depression in the general population. METHOD: Consecutive patients admitted to hospital following their first myocardial infarction were interviewed with the Schedule for Clinical Assessment in Neuropsychiatry to detect psychiatric disorders and the Life Events and Difficulties Schedule to assess recent stress. Participants completed the Hospital Anxiety and Depression Scale (HADS) at entry to the study and 1 year later and the risk factors associated with a high score at both times were assessed. RESULTS: Of 314 (88% of eligible) patients who were recruited, 199 (63%) were male and 63 (20%) had depressive disorders. Logistic regression identified the following as independently associated with depressive disorder that had been present for at least I month before the myocardial infarction: younger age, female sex, past psychiatric history, social isolation, having marked non-health difficulties and lack of a close confidant. At follow-up 269/298 (90%) responded; of 189 participants not depressed at first assessment, 39 (21%) became depressed by the 1 year follow-up. Logistic regression identified frequent angina as the only significant predictor of raised HADS scores at 12 months. CONCLUSIONS: Depression developing during the year following myocardial infarction does not have the same risk factors as that which precedes myocardial infarction. Further clarification of the mechanisms linking depression to poor outcome may require separation consideration of pre- and post-myocardial infarction depression, and its risk factors.