In the Cambridge Study in Delinquent Development, 411 South London males have been followed up from age 8 to age 32. The most important childhood (age 8-10) predictors of delinquency were antisocial child behaviour, impulsivity, low intelligence and attainment, family criminality, poverty and poor parental child-rearing behaviour. Offending was only one element of a larger syndrome of antisocial behaviour that arose in childhood and persisted into adulthood. Marriage, employment and moving out of London fostered desistance from offending. Early prevention experiments are needed to reduce delinquency, targeting low attainment, poor parenting, impulsivity and poverty.