BACKGROUND Children born to HIV-infected mothers are at risk for neurodevelopmental delay. Little is known about the neurodevelopmental outcomes of infants and toddlers born to HIV-positive mothers but who were not themselves infected by HIV, especially in poor rural areas. This study was conducted to compare developmental outcomes between young children who were HIV exposed but uninfected (HEU), and their HIV unexposed and uninfected (HUU) peers in rural Yunnan, China. METHODS A total of 250 HEU children aged 6-36 months and 250 HUU children matched for age, gender and residency were recruited from rural Yunnan, China. Neurodevelopmental outcomes were measured using Bayley Scales of Infant and Toddler Development-Third Edition (Bayley III). Multivariate analysis was performed to adjust for potential confounding effects of caregiver demographic data, maternal health status, birth outcome and children's health status. RESULTS HIV exposed but uninfected children had significantly lower composite scores in Bayley III assessment than HUU children (in the cognitive domain: 90.34 vs 92.75, P