OBJECTIVE To evaluate cognitive and academic functioning in survivors of pediatric bone marrow transplants (BMTs) at 1 and 3 years after a BMT. METHODS In a prospective, longitudinal design, patients underwent a comprehensive battery of neurocognitive measures before admission for transplantation and at 1, 3, and 5 years after a BMT. This article describes a cohort of 102 survivors with follow-up data available for 1 year after a BMT, including 54 survivors with follow-up available for 3 years. This represents the largest cohort of pediatric BMT survivors yet reported in a prospective study. RESULTS In the cohort as a whole, there were no significant changes on global measures of intelligence (intelligence quotient [IQ]) and academic achievement at either 1 or 3 years after a BMT, despite adequate power to detect an IQ change of three points or greater. Likewise, performance on specific tests of neuropsychologic function remained stable. No significant differences were observed between patients whose conditioning regimen included total-body irradiation (TBI) and those whose did not. The primary predictor of neurocognitive outcome was patient age, with younger patients more likely to show declines over time. The subset of patients who were less than 3 years of age at the time of transplantation seemed to be particularly vulnerable to cognitive sequelae. CONCLUSIONS The use of BMTs with or without TBI entails minimal risk of late neurocognitive sequelae in patients who are 6 years of age or older at the time of transplantation. However, patients who are less than 6 years of age at the time of transplantation, and particularly those less than 3 years of age, seem to be at some risk of cognitive declines.