This article reviews a range of risk factors for aggression at age 11 derived from a prospective longitudinal study on the social development of children in a large multi-ethnic sample in Switzerland. The study uses a multi-informant approach that permits reliance on combined measures of social behaviour and covers factors derived from a wide range of risk domains. Besides analysing the effects of individual risk factors, the study also investigates the effect size of cumulative risk within and across risk domains. It further analyses gender differences in risk vulnerability. Results suggest that proximal behavioural and psychological risk factors most strongly predict later aggression, whereas more distal external factors related to the family, to school and to peer relationships are less predictive. The most distal factors (perinatal risks and sociodemographic factors) are only marginally associated with later aggression. Analysis of cumulative risk suggests a strong relationship between the number of risk factors and later aggression. Finally, results support the notion of a higher risk vulnerability of boys compared with girls. Results are discussed in the context of extant research.