The purpose of this review is first to present current longitudinal data on the developmental outcome of children born to drug dependent women maintained on methadone and, second, to focus on methodological problems within this area of research. Five longitudinal studies which evaluated methadone exposed infants throughout the first two years of life are reviewed. The results of these studies suggest that no long term developmental sequelae are directly associated with methadone exposure in-utero. Although differences were often found between methadone exposed infants and comparison infants on the Bayley Scales of Infant Development, scores for the methadone exposed infants were well within the normal range of development. Existing data on methadone exposed children at 4 years of age are reviewed. No differences in cognitive performance were found between methadone exposed and comparison children although scores for both groups were low. Problems with confounding variables and the inappropriate use of a main effects model of development in this area of research are addressed and the need to investigate socioenvironmental risk factors in order to fully understand the development of children exposed to methadone in-utero is discussed.