Numerous studies have reported that HIV-infected pregnant women are at increased risk of delivery of low birth weight (LBW) infants, of preterm deliveries and of intrauterine growth restriction. The objective of the study was to determine the effect of maternal HIV infection on the anthropometric characteristics of the babies at birth. A prospective study was carried out at the Lagos University Teaching Hospital, Nigeria. There were three times more LBW babies in the HIV-positive group than in the uninfected mothers (odds ratio = 3.47, 95% confidence interval = 1.69, 7.27; chi(2) = 12.99, P = 0.0003).The maternal weight (t = 15.85; P = 0.0001), maternal body mass index (BMI) (t = 15.07; P = 0.0003), birth weight of infants (t = 27.17; P = 0.0001) and birth length (t = 31.20; P = 0.001) were significantly less in HIV-positive mothers than in controls. In conclusion, poor maternal bodyweight and low BMI are significant contributors to LBW in HIV-infected women. Nutritional counselling, dietary intake and weight monitoring during pregnancy should be emphasized to improve pregnancy outcome in HIV-infected women.