The objective of this study was to determine mother to child HIV transmission rates at different time points in a breastfeeding cohort enrolled in a single dose nevirapine program in Harare, Zimbabwe. Between 2002-2004, 434 HIV-positive mothers and their infants were recruited and followed up from delivery to 15 months. Infant blood specimens were collected for HIV testing at these time points. The majority of the patients (78%) received single dose nevirapine. The overall HIV transmission rate was 21.8% (17.8-25.8). Receiving single dose nevirapine was protective against HIV vertical transmission although statistically insignificant (relative risk: 0.76; 95% CI: 0.49-1.19). Breastfeeding was not found to be associated with HIV vertical transmission (P = 0.612). In this resource-limited setting, HIV transmission rates are high. Efforts to use more efficacious regimens to arrest HIV vertical transmission are required.