In a longitudinal study, the prevalence of post partum depression was investigated in 293 women. They were assessed during gestation at 32 weeks, and consecutively after parturition with an interval of six weeks from four weeks until 34 weeks' post partum. The prevalence of post partum depression (RDC) varied between seven and 14%, with a peak at ten weeks' post partum. It was found that women were depressed significantly more often at ten weeks' post partum compared with pregnancy, the first post partum weeks and the later post partum period. This finding suggests that it is not directly after parturition that women are more prone to depression. The relationship between variables such as blues, parity, PMS and depression showed that at different assessments in the post partum period different women are depressed, women who do not necessarily share the same characteristics. This finding may explain why in some studies a relationship was found between certain kinds of variables and post partum depression while in others not. PMS was found to be significantly related to post partum depression only at the time of the women resumed menstruation. It is suggested that screening on post partum depression partly involves screening on depressive symptoms related to PMS.