The physical and neurobehavioral findings at 3 years of age for 39 children born to mothers on methadone- maintenance and 23 children born to drug-free comparison mothers are reported. The methadone children had a higher incidence of head circumferences less than the third percentile, nystagmus/strabismus, and otitis media. No differences were found in number of emergency room visits, infections, or hospitalizations. Mean scores on the Merrill-Palmer Scale of Mental Tests were not significantly different, but more methadone children had scores less than the 25th percentile. Spontaneous language production was low in both groups of children. The neurological evaluation and head circumference correlated with the Merrill-Palmer scores. It is concluded that methadone affected some children more adversely than others, but it is important to examine how psychosocial and environmental factors interact with methadone maintenance in shaping development. Includes 11 references. (JDD)