Depending on the way it is defined depression can be seen as a state of mood, as a symptom, as a syndrome or as a clinical diagnosis. Epidemiological studies show that depression is the most common mental disorder in man. Up to 4 % of men and 8 % of women suffer from a clinically significant depressive disorder, while depressive symptoms are much more common. The occurrence of depression is associated with factors such as age, marital status, social class, and social conditions. In Finland, only one third of persons suffering from depression are actually being treated for their disorder.