Since 1978, a prospective investigation has been underway to study the consequences of prenatal exposure to a number of widely used drugs. Data are presented describing some of the associations between maternal use of cigarettes and marijuana and effects upon the offspring beyond the newborn stage. At one month of age, prenatal cigarette exposure was associated with hypertonicity and increased nervous system excitation while prenatal marijuana exposure was associated with symptoms similar to mild narcotic withdrawal. At 12 months of age, maternal cigarette smoking was significantly associated with lower mental scores and altered responses to auditory items. At 24 months, similar associations were noted although the unique predictive power of maternal smoking was overshadowed by the influence of the postnatal environment. In the one and two year old offspring of the marijuana users, no association was noted between drug use and motor, mental or language outcome variables. At three years of age a dose response relationship between lower language scores, lowered cognitive scores and prenatal cigarette exposure was noted. At this age, some cognitive and language deficits were also observed with prenatal marijuana exposure. Overall, it appears that at one, two and three years of age, there are persistent effects of prenatal exposure to cigarettes but the effects of prenatal marijuana exposure, if present, are not as readily ascertained.