Background: A negative effect of prenatal zinc deficiency on brain function has been well established in experimental animals, but this association in humans is controversial. Objective: 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. Design: 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. Results: 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/m2) < 26.0 in the original trial. No differences in the scores were found between these subgroups. Conclusions: 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.