A negative effect of prenatal zinc deficiency on brain function has been well established in experimental animals, but this association in humans is controversial. We evaluated the effect of prenatal zinc supplementation on the mental and psychomotor development of 355 children whose mothers participated in a double-blind trial of zinc supplementation that resulted in increased head circumference and birth weight. The children took 6 tests-the Differential Ability Scales, Visual Sequential Memory, Auditory Sequential Memory, Knox Cube, Gross Motor Scale, and Grooved Pegboard tests-at a mean age of 5.3 y. The scores were compared between the children of women who received a daily oral dose of 25 mg Zn during the second half of pregnancy and the children of women who received placebo. There were no differences in the test scores of neurologic development between the 2 groups. We analyzed the scores in 4 subgroups on the basis of maternal body mass index, because the increases in birth weight and head circumference due to the supplementation occurred only in the children of women with a body mass index (in kg/m(2)) < 26.0 in the original trial. No differences in the scores were found between these subgroups. Zinc supplementation of women in the latter half of pregnancy had no effect on the neurologic development of their children at age 5 y. It is not known whether our findings of no positive effect in the population with apparently inadequate zinc nutriture can be readily extrapolated to other populations.