A risk factors conceptual framework was employed to determine the relative contributions of ecological risk factors in antisocial behaviour (operationalised as substance misuse and criminality) among youth gangs (N=197) and prison inmates (N=821) in Nigeria. A mixed method (quantitative and qualitative) was adopted. Two preliminary studies were conducted (and results reported) to pilot the reliability and validity of the instruments before undertaking field studies in Nigeria. The results of the main studies revealed that ecological risk factors (i.e., individual, societal and community variables) are predictors of substance misuse and criminality. A mediation analysis successfully predicted lack of support, peer pressure and impulsivity to have significant effects on substance misuse and criminality among the youth gangs. Similar statistical significant mediation effects were found in relation to poverty and impulsivity on substance misuse and criminality among the prison inmates. Taken together, the findings suggested models developed in a Euro-American cultural context do mostly transfer to the African sub continent. However, prevention or intervention strategies based on ecological risk factors should meet up with the practical reality and resources obtainable in the African context. The implications of the findings on risk-focused prevention in countries targeting individuals who are at risk of engaging in antisocial behaviour are discussed.