This study compares the first year's health, neurodevelopmental status, and environment of infants of drug-dependent mothers attending methadone programs during pregnancy with those of drug-dependent mothers not enrolled in treatment programs (untreated). Both groups were also compared with drug-free controls. During pregnancy, the use of heroin and other psychoactive drugs was common among patients using methadone. Neonatal abstinence syndrome was of longest duration in the methadone group. Infants of both drug groups were smaller at birth, had more neonatal infections, and were viewed as more difficult to care for after nursery discharge than were those of drug-free mothers. On follow-up, mean developmental scores were within the normal range for all groups. The untreated drug-dependent group was more hypertonic than the methadone group, and a high rate of transient or minor motor disturbances and poor attention span was found in both drug groups. The behavior of methadone-treated women during pregnancy and the postnatal period closely resembled that of drug-free controls, and contrasted with untreated drug-dependent women. Methadone-treated women had a high degree of compliance with antepartum care, and 80% continued in the role of parent through the first year. Further investigation will determine whether the consistency of parenting will continue and whether it will enhance the development of their children.