This paper examines mental health service use among publicly insured white and African-American pregnant and postpartum women who live in a metropolitan area. The study examines the extent to which ethnicity, physical health problems, and behavioral health risk factors are associated with the probability of service use during the prenatal-postpartum period. It also analyzes the patterns of service utilization for those women who used mental health services. Medicaid claims and eligibility data, County Reporting System claims and admissions data, and Pennsylvania State Vital Birth Records were integrated using a unique algorithm. Logistic regression was employed to estimate the probability of mental health service use among 3,841 low-income women residing in Philadelphia who were continuously enrolled in Medicaid for 9 months preceding delivery and 6 months postpartum. Analyses were also conducted on the intensity and location of service use, as well as psychiatric diagnosis, during pregnancy and the postpartum period. About 10% of the women used mental health services during the study period. Women were more likely to use services if they were Caucasian, had a number of chronic diseases, had a number of pregnancy complications, and smoked. Among users, the same proportion (ca. 6%) used services during pregnancy and postpartum, with the average number of outpatient visits slightly higher during pregnancy than during the postpartum period. Most outpatient services (86%) were delivered in the specialty sector. Most women who used mental health services (84%) were diagnosed with minor psychiatric disorders including minor depression and anxiety disorders. Women who used services during the postpartum only were more likely to be diagnosed with major depression, whereas women who used services throughout the perinatal period were more likely to be diagnosed with severe mental disorders. Health providers can use information generated in this study to identify women who are likely to have a need for mental health services.