Depression is a common disorder in the general population. However, its prevalence among patients attending various health-care facilities is less well known. There have been very few Finnish studies of this topic. The Tampere Depression Project (TADEP) dealt with the prevalence of depression and factors associated with it in individuals seen in community health centres (CHC) and in psychiatric-service (PS) patients. The diagnosis of depression was based on a standardized Present State Examination interview and a DSM-III-R assessment, carried out on 436 CHC patients and 428 PS patients. The severity of depression was assessed using the Hamilton Rating Scale of Depression. About 10% of CHC patients and 50% of PS patients suffered from clinical depression. In addition to these, some depressive symptoms were displayed by just under 10% of subjects. Similar prevalence rates were obtained by the various methods used. The 1-year prevalence rate of clinical depression was 20% for the CHC patients and almost 60% for the PS patients. Mild depression represented the largest group. In the CHC group, depression was found more often in middle-aged and widowed subjects and in patients with a lower educational level and blue-collar workers than in others. In the PS group, depression was found more often in women, the oldest subjects and the widowed than in others.