The prevalence of childhood maltreatment and the magnitude of the association of maltreatment with internalizing mental health symptoms were examined in 398 incarcerated youth. The prevalence of abuse greatly exceeded general population rates. The proportion of variance in mental health symptoms accounted for by maltreatment was small but developmentally significant. Sexual abuse is a markedly stronger predictor of internalizing mental health problems in incarcerated youth than physical abuse. Consistent with a bio‐psychological model of trauma, dissociation at the time of sexual abuse was the strongest nondemographic predictor of mental health symptoms. Physical abuse was associated with more internalizing mental health problems for children from families with mental health problems and families with lower socioeconomic status. Implications for practice and research are discussed.