In this second review article, several aspects of winter depression are reviewed: prevalence, etiology and pathogeneses. Prevalence figures in Europe are lower than those in the USA. Prevalence figures in the USA may be related to latitude, in Europe there is no evidence for this kind of relationship. Research of the etiology and pathogeneses of winter depression is still inconclusive. Finally, a review is given of research of predictors of successful light treatment and follow-ups into the stability of the diagnosis of winter depression over time.