In a double-blind trial in Dar es Salaam, Tanzania, 8468 pregnant women, who were negative for human immunodeficiency virus infection (HIV-negative), were randomly assigned to receive daily multivitamins (including multiples of the recommended dietary allowance) or placebo. All the women received prenatal supplemental iron and folic acid (IFA). The incidence of low birth weight (LBW) was significantly lower (7.8%) among the infants in the multivitamin group compared to those in the placebo group (9.4%). The mean difference in birth weight between the groups was modest but statistically significant. Supplementation reduced both the risk of a birth size that was small for gestational age (SGA) (10.7%) in the multivitamin group vs. 13.6% in the placebo group and the risk of maternal anemia although the difference in the mean hemoglobin levels between the groups was small. Multivitamin supplementation had no significant effects on prematurity or fetal death.