Sociodemographic disadvantage has pervasive effects on a broad range of youth outcomes, including greater likelihood of involvement in delinquent and criminal behaviours. Sociodemographic vulnerabilities rarely exist in isolation however, and research suggests that the cumulative impact of these risks exacerbates their effects. Most research examining cumulative disadvantage combines sociodemographic risk factors with more proximal variables related to individual characteristics, family functioning, social interactions and so on, disallowing exploration of the processes through which sociodemographic disadvantage operates. This paper proposes a framework for conceptualising and assessing cumulative sociodemographic risk (CSR) during adolescence using a summed index that consists only of sociodemographic risk factors known to influence antisocial involvement. Results showed that antisocial behaviours increased in line with levels of CSR. CSR was a significant predictor of adolescent antisocial behaviour in a regression model that controlled for the sociodemographic risk factors of which the index is made up, demonstrating the compounded impact of multiple simultaneous sociodemographic adversities. Findings highlight the need to recognise the effects of cumulative sociodemographic disadvantage, further explore the mechanisms through which it operates, and consider strategies for reducing its impact on outcomes such as antisocial behaviour for young people.