Mental disorders during childhood and adolescence negatively affect young people’s development and can give rise to long-term consequences. Child and adolescent mental disorders also yield longstanding costs to society that are multiplied by the loss of economic productivity in adulthood. Longitudinal studies have associated externalizing behavior problems with subsequent risk behaviors such as substance use, delinquency, violence, or financial struggles multiple times. Regarding German children and adolescents, only little is known about the subsequent risk behaviors associated with externalizing behavior problems in childhood and adolescence. This study reports on the long-term consequences in early adulthood based on data from the longitudinal BELLA study (the mental health module of the German National Health Interview and Examination Survey for children and adolescents). We examined a sample of N = 629 children and adolescents aged 12-17 years with externalizing behavior problems. Data were taken from the BELLA study at baseline and a follow-up assessment conducted 6 years later. The risk of externalizing behavior problems in childhood and adolescence for long-term consequences (problematic alcohol use, illegal drug use, delinquency, propensity to violence, financial struggles) in early adulthood was assessed by means of odds ratios and 95% confidence intervals. Population-attributable risk percentages were calculated to evaluate the degree to which externalizing behavior problems are accountable for the occurrence of long-term consequences. Several multiple logistic regressions were computed with each of the risk behaviors as outcome and with age, gender, socioeconomic status, and internalizing problems as control variables. German children and adolescents with externalizing behavior problems (n = 116) significantly more often reported long-term consequences in early adulthood than did children and adolescents without externalizing behavior problems. Six years later, 27.6% (n = 32) of the children and adolescents with externalizing behavior problems reported problematic alcohol use and 13.8% (n = 16) illegal drug use. Further, 19% (n = 22) showed delinquency, 41.4% (n = 48) showed propensity to violence, and 29.3% (n = 34) reported financial struggles. After controlling for age, gender, socioeconomic status, and internalizing problems, the at-risk group for problematic alcohol use, delinquency, and propensity to violence included boys with externalizing behavior problems from families with a lower socioeconomic status. Illegal drug use was correlated with externalizing behavior problems only. Financial struggles correlated with older age and lower socioeconomic status. Up to 16.5% of the cases with long-term consequences could be ascribed to externalizing behavior problems. These findings illustrate the necessity to identify children and adolescents at risk and to place greater emphasis on early prevention services.