Undernutrition in infancy and early childhood is thought to adversely affect cognitive development, although evidence of lasting effects is not well established. With the use of data from the Cebu Longitudinal Health and Nutrition Study, we assesshere the relationship between stunting in the first 2 y of life and later cognitive development, focusing on the significance of severity, timing and persistence of early stunting. The sample included > 2000 Filipino children administered a cognitive ability test at ages 8 and 11 y. Stunting status was determined on the basis of anthropometric data collected prospectively between birth and age 2 y. Children stunted between birth and age 2 y had significantly lower test scores than nonstunted children, especially when stunting was severe. The shortfall in test scores among children stunted in the first 2 y was strongly related to reduced schooling, which was the result of a substantial delay in initial enrollment as well as higher absenteeism and repetition of school years among stunted children. Interactions between stunting and schooling were not significant, indicating that stunted and nonstunted children benefitted similarly from additional schooling. After multivariate adjustment, severe stunting at age 2 y remained significantly associated with later deficits in cognitive ability. The timing of stunting was also related to test performance, largely because children stunted very early also tended to be severely stunted (chi(2) P = 0.000). Deficits in children's scores were smaller at age 11 y than at age 8 y, suggesting that adverse effects may decline over time. Results emphasize the need to prevent early stunting and to provide adequate schooling to disadvantaged children.