Postnatal depression is a significant problem affecting 10-15% of mothers in many countries and has been the subject of an increasing number of publications. Prenatal depression has been studied less. The aims of the present investigation were: 1) to obtain information on the prevalence of prenatal and postnatal depression in low income Brazilian women by using an instrument already employed in several countries, i.e., the Edinburgh Postnatal Depression Scale (EPDS); 2) to evaluate the risk factors involved in prenatal and postnatal depression in Brazil. The study groups included 33 pregnant women interviewed at home during the second and third trimesters of pregnancy, and once a month during the first six months after delivery. Questions on life events and the mother's relationship with the baby were posed during each visit. Depressed pregnant women received less support from their partners than non-depressed pregnant women (36.4 vs 72.2%, P<0.05; Fisher exact test). Black women predominated among pre-and postnatally depressed subjects. Postnatal depression was associated with lower parity (0.4 ± 0.5 vs 1.1 ± 1.0, P<0.05; Student ttest). Thus, the period of pregnancy may be susceptible to socioenvironmental factors that induce depression, such as the lack of affective support from the partner. The prevalence rate of 12% observed for depression in the third month postpartum is comparable to that of studies from other countries.