Drug use during pregnancy is common and the developing foetus may be exposed to a range of environmental toxins that have long-term consequences for neurodevelopment. We conducted a systematic review of the literature to explore the results of longitudinal cohort studies that have examined this question. Out of 2,977 abstracts identified, 7 previous systematic reviews and 95 original articles met further selection criteria. These mostly addressed the neurodevelopmental effects of exposure to lead, polychlorinated biphenyls, mercury, cocaine, alcohol, marijuana, cigarettes and antidepressants. Radiation, opiates, steroids, amphetamines and caffeine have received much less attention. Findings are difficult to interpret because risk factors tend to cluster together and interact. However, some findings are consistent. Lead and PCB's have a general effect on brain development, whilst marijuana and alcohol appear to have long-term effects specifically on attentional skills. The effects of alcohol increase with maternal age and binge drinking is more important than average intake. The effects of cocaine diminish with age and are largely mediated through psychosocial factors, whilst the relation between smoking and later delinquency is largely mediated by genetically inherited factors. Exposure to toxins during pregnancy may constitute an important but relatively unacknowledged cause of child psychiatric morbidity.