Studies on the long-term developmental effects of in utero cocaine exposure are few and the small number of studies published do not consider the postnatal environment. The present investigation was conducted to quantify the role that postnatal environment played compared to prenatal exposure. Four groups of 25 infants, each assessed at 12 months of age, were included in the study design: 1) noncocaine-exposed children residing with their biological parents in low socioeconomic environments, 2) cocaine-exposed children living with their biological parents in low socioeconomic environments, 3) noncocaine-exposed children adopted at birth in middle to upper-middle socioeconomic environments, and 4) cocaine-exposed children adopted at birth. Infants were assessed by the Uzgiris-Hunt Ordinal Scales of Infant Psychological Development, the Fagan Test of Infant Intelligence, and the Infant Monitoring Questionnaire. Height and head circumference were measured. Gender and ethnicity were controlled statistically. Significant differences were found in cognitive functioning, in fine motor development, and in physical growth between control and prenatally cocaine-exposed children. Adoption enhanced cognitive functioning and fine motor skills among infants not exposed to cocaine prenatally, but had no apparent effect on infants prenatally exposed to cocaine. Am. J. Hum. Biol. 12:417-428, 2000. Copyright 2000 Wiley-Liss, Inc.