We reviewed adverse event (AE) data in the National Cooperative Growth Study from start-up (1985) until January 1, 1999. Enrollment was 33,161. A total of 2,632 AE reports were received; 863 were serious events, with 156 deaths. The most common cause of death was recurrence of intracranial neoplasm. There were 20 reports of leukemia, and the standard morbidity ratio (SMR) was 0.73 (95% CI: 0.20-1.86) for the four cases without risk factors. There were 35 reports of extracranial nonleukemic malignancy, and the SMR was 0.44 (95% CI: 0.24-0.74) for the 14 cases without risk factors. The recurrence rate for all brain tumors present at baseline was 7.6%, and for craniopharyngiomas, 6.4%. There were 49 reports of intracranial hypertension (20 patients had papilledema), 68 reports of diabetes/hyperglycemia, 45 of slipped capital femoral epiphysis, 136 of scoliosis, and five of pancreatitis. There was no evidence of increased incidence of leukemia or extracranial nonleukemic malignancies among patients without prior risk factors. Intracranial hypertension does not necessarily occur early in growth hormone therapy. Other findings were consistent with past observations.