Women with HIV have higher rates of psychiatric disorders than HIV-negative women, yet little is known about their postpartum mental health and associated service use. The purpose of this study was to characterize HIV-positive women's use of ambulatory and acute mental health services in the first year postpartum, relative to HIV-negative women. Using health administrative data, we identified 861,365 women who had a live birth delivery from April 1, 2002 to March 31, 2012 in Ontario, Canada, of whom 530 were identified to be HIV-positive. We described their use of mental health services, including outpatient mental health visits, psychiatric emergency department (ED) visits and hospitalizations using adjusted odds ratios (aORs) and 95% confidence intervals (CIs). HIV-positive women were more likely to access outpatient mental health services (31.5% vs. 21.0%, aOR, 1.26; 95% CI, 1.03-1.55), but more likely to remain engaged in psychiatrist services only (15.6% vs. 6.5%, aOR, 2.35; 95% CI, 1.41-3.72). They were also more likely to require a psychiatric ED visit or hospitalization (3.3% vs. 1.1%, aOR, 2.74; 95% CI, 1.72-4.12). Our findings highlight the importance of considering postpartum mental health as part of comprehensive reproductive health care for women with HIV.