To estimate whether there is a temporal association between Postpartum Depression (PPD) and intimate partner violence (IPV), and to assess the potential role of social support on this relationship. A cross-sectional study was conducted between January 2006 and March 2007 with 701 low income women who received prenatal and postpartum care in primary health care units of the public sector in São Paulo, Brazil. The Self-Report Questionnaire (SRQ-20) was used to assess the presence of PPD. Structured standardized questionnaires were used to assess IPV and social support. The prevalence of PPD was estimated with a 95 % confidence interval. Crude and adjusted prevalence ratios were calculated using Poisson regression to examine the association between PPD and exposure variables. Values of p < 0.05 were considered statistically significant. The prevalence of PPD was 27.9 % (95 %CI 24.6:31.2). The prevalence of psychological IPV was 38.6 %, physical IPV 23.4 %, and sexual IPV 7.1 %. The multivariate analysis showed that PPD was strongly associated with current psychological and physical/sexual violence, after controlling for confounding factors, and less so with past (prenatal or lifetime) IPV. Presence of social support was an independent protective factor for PPD. Identifying and addressing intimate partner violence, including psychological violence, in the postpartum period should be considered as part of a comprehensive approach to caring for new mothers.