Aspects of neurobehavioural development were examined in 28 school-age children born to regular cannabis users and 28 control children matched on prenatal drug history. Measures which discriminated between the study groups and on which the children of cannabis users scored more poorly included parental ratings of behaviour problems, visual-perceptual tasks, language comprehension, and distractibility. For a measure of visual memory and a measure of language comprehension, mother's age at the child's birth potentiated the effect of cannabis use to produce lowered scores for children of young, cannabis-using mothers relative to children of young, nonusing mothers. After controlling for the influence of mother's age at delivery, mother's personality and home environment, the relationship between prenatal cannabis exposure and the discriminating variables was no longer statistically significant. Path analysis demonstrated the way in which home environment conditions, particularly high levels of aggression, could magnify effects of prenatal exposure to cannabis on postnatal outcomes.