BACKGROUND: The long-term impact of early malnutrition on human capital outcomes remains unclear, and existing evidence has come largely from observational studies. OBJECTIVE: We compared the impact of a nutritional supplement given during pregnancy or lactation in rural Gambia on educational performance and cognitive ability in offspring at their maturity. DESIGN: This study was a follow-up of a randomized trial of prenatal high protein and energy supplementation conducted between 1989 and 1994. Subjects were 16-22 y of age at follow-up, and information was collected on schooling achievement and cognitive ability by using the Raven's progressive matrices test, Mill Hill vocabulary test, and forward and backward digit-span tests. RESULTS: A total of 1459 individuals were traced and interviewed and represented 71% of the original cohort and 81% of the surviving cohort. There was no difference in cognitive ability or educational attainment between treatment groups by using any of the methods of assessment. CONCLUSION: We have shown little evidence to support a long-term effect of prenatal protein-energy supplementation compared with supplementation during lactation on cognitive development in rural Gambians. This trial was registered at http://www.controlled-trials.com as ISRCTN72582014.