Highly active antiretroviral therapy (HAART) has changed the morbidity pattern affecting HIV-infected individuals to include non-AIDS-defining cancers. We describe the breast cancer cases occurring in a cohort of 860 HIV-infected women followed in Rio de Janeiro, Brazil, and estimate the incidence rate of breast cancer for this population. Nine cases were identified; median age at diagnosis was 46 years. Median survival after breast cancer diagnosis was 12 months. Breast cancer diagnosis was made within 2 to 15 years of HIV-infection diagnosis. At breast cancer diagnosis, CD4 counts ranged from 135 to 782 cells/mm3; six women were receiving HAART. Histological analysis indicated infiltrating ductal carcinoma in all cases. The incidence rate of breast cancer was 133 cases per 100,000 persons-year. Patients from our case series were late diagnosed with breast cancer and thus suffered from worse prognosis. Strategies targeting earlier diagnosis and prompt initiation of treatment are needed.