Antisocial behaviour in adolescence can be associated with ill health in the form of self-harm, drug abuse, and mental disorders, and may presage criminal activity later in life. This is a worldwide problem with far-reaching social and economic implications, for individuals as well as for society as a whole. There are both genetic and environmental risk factors associated with antisocial behaviour, and recent research appears to show a substantial genetic eff ect on the likelihood of an individual becoming a persistent off ender. This is potentially a controversial fi nding, and some will inevitably draw the conclusion that individuals who commit crimes do so not of their own errant free will but because they have been genetically programmed to do so. But before we accept this startling conclusion the paper needs careful scrutiny. James Barnes and co-workers studied people who had participated in a longitudinal survey of adolescent health in the USA. The authors compared the self-reported behaviour of adolescents, in particular twins, siblings, and other relatives, assessing frequency of antisocial behaviours—ranging from unruly conduct in public to drug dealing—over a 6-year period during the transition from adolescence to young adulthood. The results yielded a heritability statistic of 56–70%, suggesting that most of the diff erences in an individual’s reported antisocial behaviour could be ascribed to genetics. This seems a high degree of heritability, and it should be remembered that misleading associations are not unknown in individual genetic studies. Indeed, environmental and genetic eff ects are not independent—nature and nurture are interrelated, and infl uence each other substantially. Large numbers of genes, possibly thousands, are likely to have small but cumulative eff ects on behaviour, and might only manifest in antisocial behaviour when combined with environmental factors. Just as individuals genetically predisposed to addiction are not guaranteed to abuse drugs, the law-breakers of the future are likely to be made rather than born antisocial. It is highly unlikely that future research will be able to identify a hypothetical gene or genes conferring criminality on unfortunate recipients, so genetics will probably not be able to improve crime detection and prevention for the maintenance of law and order. Barnes and colleages’ study does, however, highlight the need to study environmental and behavioural associations with ill health in adolescents in order to shape health and social policies. The importance of tackling poverty, drug use, and child maltreatment as risk factors for crime has never been clearer.