BACKGROUND: Global coverage of prevention of mother-to-child (PMTCT) services reached 53% in 2009. However the number of pregnant women who test positive for HIV in antenatal clinics and who link into long-term HIV care is not known in many resource-poor countries. We measured the proportion of HIV-positive pregnant women in Mwanza city, Tanzania, who completed the cascade of care from antenatal HIV diagnosis to assessment and engagement in care in adult HIV clinics. METHODS: Thirty antenatal and maternity ward health workers were interviewed about PMTCT activities. Nine antenatal HIV education sessions were observed. A prospective cohort of 403 HIV-positive women was enrolled by specially-trained clinicians and nurses on admission to delivery and followed for four months post-partum. Information was collected on referral and attendance at adult HIV clinics, eligibility for highly active antiretroviral therapy (HAART) and reasons for lack of attendance. RESULTS: Overall, 70% of PMTCT health workers referred HIV-positive pregnant women to the HIV clinic for assessment and care. Antenatal HIV education sessions did not cover on-going care for HIV-infected women. Of 310 cohort participants tested in pregnancy, 51% had received an HIV clinic referral pre-delivery. Only 32% of 244 women followed to four months post-partum had attended an HIV clinic and been assessed for HAART eligibility. Non-attendance for HIV care was independently associated with fewer antenatal visits, poor PMTCT prophylaxis compliance, non-disclosure of HIV status, and non-Sukuma ethnicity. CONCLUSION: Most women identified as HIV-positive during pregnancy were not assessed for HAART eligibility during pregnancy or in the first four months post-partum. Initiating HAART at the antenatal clinic, improved counselling and linkages to care between PMTCT and adult HIV treatment services and reducing stigma surrounding disclosure of HIV results would benefit on-going care of HIV-positive pregnant women.