Infants born to HIV-infected women are at increased risk of impaired neurodevelopment, but little research has attempted to identify modifiable risk factors. The objective of this prospective cohort analysis was to identify maternal, socioeconomic, and child correlates of psychomotor and mental development in the first 18 mo of life among Tanzanian infants born to HIV-infected women. We hypothesized that child HIV infection, morbidity, and undernutrition would be associated with lower developmental status when taking into consideration maternal health and socioeconomic factors. Baseline maternal characteristics were recorded during pregnancy, birth characteristics were collected immediately after delivery, infant micronutrient status was measured at 6 wk and 6 mo, and anthropometric measurements and morbidity histories were performed at monthly follow-up visits. The Psychomotor Development Index (PDI) and Mental Development Index (MDI) of the Bayley Scales of Infant Development, 2nd edition (BSID-II) were used to assess developmental functioning at 6, 12, and 18 mo of age. Multivariate repeated regression models with time-varying covariates were used to estimate adjusted mean MDI and PDI scores for each level of the variables. A total of 311 infants contributed ≥1 BSID-II assessments for 657 PDI and 655 MDI measurements. Of infants, 51% were male, 23% were born preterm, 7% were low birth weight, and 10% were HIV-positive at 6 wk. Preterm birth, child HIV infection, stunting, and wasting were independently associated with lower PDI and MDI scores. Strategies to lower mother-to-child transmission of HIV, prevent preterm birth, and enhance child growth could contribute to improved child psychomotor and mental development.