Background: Previous reports have suggested that prophylactic indomethacin decreases cerebral blood flow and may play a role in the development of ischemic brain injury and developmental handicaps. Objective: To assess the neurodevelopmental outcome of subjects at 36 months' corrected age (CA) who, as low-birth-weight infants, received prophylactic low-dose indomethacin within the first 24 hours of life to prevent patent ductus arteriosus. Setting: Newborn intensive care nursery and outpatient follow-up clinic at Children's Hospitals and Clinics of Minneapolis, Minneapolis, Minn. Design: Ninety infants with birth weights of 600 to 1250 g were entered into a prospective, randomized, controlled trial to receive either prophylactic indomethacin, 0.1 mg/kg, or placebo in the first 24 hours and again every 24 hours for 6 doses to prevent patent ductus arteriosus. Nonresponders were treated with standard therapeutic indomethacin or ligation. Neurodevelopmental assessment at approximately 36 months' CA included medical and developmental histories, physical examinations, and developmental testing using the Bayley II Scales of Infant Development on subjects up to 42 months' CA. Subjects were classified as (1) normal, (2) mildly to moderately abnormal, or (3) severely impaired. Results: Forty-two (98%) of 43 subjects who received prophylactic indomethacin survived compared with 46 (98%) of 47 who received placebo. Sixty-six (75%) of 88 survivors were seen for neurodevelopmental assessment at 36 months' CA. This group included 29 (69%) of 42 who received prophylactic indomethacin and 37 (80%) of 46 who received placebo. Twenty-three (79%) of 29 infants in the prophylactic indomethacin group had normal neurodevelopmental assessments at 36 months' CA compared with 26 (70%) of 37 placebo-treated subjects (P = .68). Of 4 significantly impaired subjects treated with prophylactic indomethacin, 1 had spastic diplegia; 1, spastic quadriplegia; 1, cognitive delay; and 1, significant motor delay. Of 8 significantly impaired placebo-treated subjects, 7 had spastic diplegia; 1, microcephaly. Conclusion: The use of prophylactic low- dose indomethacin when initiated in the first 24 hours of life in low-birth- weight infants to prevent patent ductus arteriosus is not associated with adverse neurodevelopmental outcome at 36 months' CA.