SynopsisThere is some evidence to suggest that the role of genetic and environmental influences may vary for different types of psychiatric symptoms in childhood. The aim of this study was to examine to what extent genetic and environmental factors influence parent-rated conduct and neurotic symptoms in childhood and adolescence, using data obtained from a systematically ascertained sample of twins (198 same sex pairs) aged between 8 and 16 years. For symptoms of antisocial behaviour, transmission could be explained entirely by shared environmental factors. Social class effects were also found to have a significant influence on antisocial behaviour, although these effects only accounted for a small proportion of the variance explained by shared environmental factors. In contrast, transmission of neurotic symptoms was best explained by additive genetic influences alone with no contribution from shared environment. Non-shared environmental factors accounted for a substantial component of the variation for both antisocial behaviour and neurotic symptoms.