The leading cause of death in the neonatal period is respiratory failure, and extracorporeal membrane oxygenation (ECMO) is an effective means of improving survival in select patients. Only neonates with severe hypoxia and acidosis are treated with ECMO. To determine the developmental outcome of the neonates we supported with ECMO, we reviewed the records of all our patients who are at least 6 months of age. The results of follow-up assessment were available for 57 patients and growth parameters were available for 43 patients. Examinations were done at 6 to 48 months (mean, 22.1). Growth parameters showed that 14% of the patients were below the tenth percentile for height and weight while 16.3% were below the tenth percentile for head circumference. Twenty-four patients were evaluated using the Bayley Scales of Infant Development consisting of a Mental Developmental Index (MDI) and a Psychomotor Developmental Index (PDI). Normal scores (greater than 84) were obtained in 75% on the MDI and in 88% on the PDI. Only two patients (8%) scored less than 85 on both portions. Twelve patients were evaluated using the McCarthy Scales of Children's Abilities. The mean score was 95 and nine patients (75%) had scores greater than 85. The Gessell was used to evaluate six patients and five were normal. The Denver Developmental Screening Test was used to evaluate 23 patients and all passed. The results of neurologic examination were documented in 57 patients. One patient had severe spastic quadriplegia with cerebral palsy. The neurological examination was normal in the other patients. Only one of 57 patients is profoundly delayed (2%) and 45 (79%) are normal.(ABSTRACT TRUNCATED AT 250 WORDS)