Background: Adolescents in the child welfare and juvenile justice systems show high rates of substance-use disorders. Yet, little is known about the association between childhood adversities and impulsive behavior involving substance-use disorders in shared residential care in the child welfare and juvenile justice systems. Objective: The aim of this study is to investigate the prevalence of substance-use disorders and their association with childhood adversities and impulsive behavior among child welfare-and juvenile justice-involved adolescents in residential care. Method: A total of 386 adolescents placed into Swiss residential care by the child welfare and juvenile justice systems (37.0% girls; age range = 10-18 years; mean age = 15.41 years) were studied. Substance-use disorders and childhood adversities were categorically assessed using the Kiddie Schedule for Affective Disorders and Schizophrenia – Present and Lifetime Version. Impulsive behavior was dimensionally measured with the Youth Psychopathic Traits Inventory. Statistical methods included descriptive analyses and logistic regression analyses. Results: Juvenile justice-involved adolescents showed higher rates of any substance-use disorder compared to child welfare-involved counterparts (38% vs. 20%; 2(1) = 22.21, p < 0.001). Higher numbers of childhood adversities were found among child welfare (U = 3039, p < 0.001) and juvenile justice (U = 309.5, p < 0.001) youths with substance-use disorders compared to those without substance-use disorders. Impulsive behavior was related to substance-use disorders among both the child welfare (B = 0.61, SE = 0.15, p < 0.001) and the juvenile justice groups (B = 0.40, SE = 0.17, p = 0.02). Conclusion: Considering the high rates of substance-use disorders in both the child welfare and the juvenile justice samples, this study highlights that treating impulsive behavior and incorporating trauma-informed care for childhood adversities may reduce substance-use disorders among youths in residential care. Implications for care system practice and avenues for future research are discussed.