In the present investigation we were interested to study the possible role of in-utero exposure to heroin and of the home environmental in the etiology of long-term developmental problems in children born to heroin-dependent parents in comparison to matched controls. The children were examined at .5-6 years of age by a developmental pediatrician and a developmental psychologist using, for the children up to 2.5 years of age, the Bayley Developmental Scales, and for children aged 3-6 years the McCarthy Scales for Children's Abilities. We examined 83 children born to heroin-dependent mothers, and compared the results to those of 76 children born to heroin-dependent fathers and to three control groups; 50 children with environmental deprivation, 50 normal children from families of moderate or high socioeconomic class, without environmental deprivation, and 80 healthy children from kindergartens in Jerusalem. There were five children (6.0%) with significant neurological damage among the children born to heroin-dependent mothers and six (7.9%) children among those born to heroin-dependent fathers. The children born to heroin-dependent mothers had a lower birth weight and a lower head circumference at examination when compared to controls. The children born to heroin-dependent parents also had a high incidence of hyperactivity, inattention, and behavioral problems. The lowest DQ or IQ among the children with cognitive levels above 70 was found in the children with environmental deprivation, next was the DQ or IQ of children born to heroin-dependent fathers, then the DQ or IQ of the children born to heroin-dependent mothers. When the children born to heroin-dependent mothers were divided to those that were adopted at a very young age and to those raised at home, the adopted children were found to function similarly to the controls while those not adopted functioned significantly lower. Our results show that the developmental delay and behavioral disorders observed among children born to drug-dependent parents raised at home may primarily result from severe environmental deprivation and the fact that one or both parents are addicted. The specific role of the in-utero heroin exposure in the determination of the developmental outcome of these children (if they do not have significant neurological damage), seems to be less important in comparison to the home environment.