This thesis describes the epidemiology of (chronic) major depression in a general population study (NEMESIS, the Netherlands Mental Health Survey and Incidence Study). The course of major depression is very heterogenous but almost 20% of those with a diagnosis of major depression have a chronic course. Illness-related factors (severity of the depressive episode, prior episodes and their duration) are the strongest predictors of a longer duration of depression. These findings have important implication for treatment.