There has been an increasing use of cocaine in North America among women of reproductive age. The potential effects of cocaine on the fetus have raised serious concerns about the health of large numbers of children exposed in utero to the drug. Using neonatal hair and urine tests for benzoylegconine (BE), we quantified the incidence of fetal exposure to cocaine among 600 babies born in 3 nurseries in Toronto from 1990-91. A total of 37 babies (6.25%) tested positive for cocaine exposure by either hair test, urine test, or both. The hair test detected 33 cases and failed to identify 4 babies who had low urine concentrations of BE. The urine test failed to identify 76% of the cases. In downtown Toronto, the overall rate of fetal exposure to cocaine was 12.5% (25/200), significantly higher than in the 2 suburban nurseries (3%; 12/400). Babies are born with hair which has grown during the last trimester of pregnancy; hence, our analysis identifies women who have used cocaine long after they became aware of pregnancy. Our figures translate to more than 5,000 babies annually in the greater Toronto area who are cared for postnatally by mothers regularly using cocaine. Because history and urine testing during delivery fail to identify the majority of these cases, most of these children are not likely to receive the appropriate medical and social services and follow-up.