Aspects of neurobehavioral development were examined in 133 36-month- and 130 48-month-old children for whom prenatal exposure to marijuana, cigarettes, and alcohol had been previously ascertained and who have been assessed since birth. Parallelling earlier observations made with this sample at 12 and 24 months, prenatal exposure to cigarette smoking was significantly associated with poorer language development and lower cognitive scores at both 36 and 48 months after statistically controlling for confounding factors. Relatively low levels of maternal alcohol consumption, which had measurable effects at 24 and 36 months, no longer had significant relationships with outcome variables at 48 months of age. At 48 months, significantly lower scores in verbal and memory domains were associated with maternal marijuana use after adjusting for confounding variables. This negative relationship is the first reported association beyond the neonatal stage, and may represent a long-term effect of the drug upon complex behavior that, at a younger age, had not developed and/or could not be assessed.