Developmental outcomes of infants of drug-dependent mothers (IDDM) who used heroin during pregnancy, alone or in combination with methadone, were unfavorable compared with outcomes of infants of mothers who were not drug dependent or infants in the general population. Unfavorable items for IDDM were: gestational age and birth weight, physical growth, neurological development, intelligence, behavior, social competences and social state (foster care). Prenatal care with social support and methadone substitution were critical factors for IDDM. The IDDM in foster care appeared to exhibit even more unfavorable outcomes than those living with their biological parents.