OBJECTIVE: To assess the impact of routine antenatal HIV testing for preventing mother-to-child transmission of HIV (PMTCT) in urban Zimbabwe. METHODS: Community counsellors were trained in routine HIV testing policy using a specific training module from June 2005 through November 2005. Key outcomes during the first 6 months of routine testing were compared with the prior 6-month "opt-in" period, and clients were interviewed. FINDINGS: Of the 4551 women presenting for antenatal care during the first 6 months of routine HIV testing, 4547 (99.9%) were tested for HIV compared with 3058 (65%) of 4700 women during the last 6 months of the opt-in testing (P < 0.001), with a corresponding increase in the numbers of HIV-infected women identified antenatally (926 compared with 513, P < 0.001). During routine testing, more HIV-infected women collected results compared to the opt-in testing (908 compared with 487, P < 0.001) resulting in a significant increase in deliveries by HIV-infected women (256 compared with 186, P = 0.001); more mother/infant pairs received antiretroviral prophylaxis (n = 256) compared to the opt-in testing (n = 185); and more mother/infant pairs followed up at clinics (105 compared with 49, P = 0.002). Women were satisfied with counselling services and most (89%) stated that offering routine testing is helpful. HIV-infected women reported low levels of spousal abuse and other adverse social consequences. CONCLUSION: Routine antenatal HIV testing should be implemented at all sites in Zimbabwe to maximize the public health impact of PMTCT.