Caffeine is the most widely used psychoactive substance in the world and currently the only one legally available to children and adolescents. The sale and use of caffeinated beverages has increased markedly among adolescents during the last decade. However, research on caffeine use and behaviors among adolescents is scarce. The authors investigate the relationship between adolescent caffeine use and self-reported violent behaviors and conduct disorders in a population-based cross-sectional sample of 3,747 10th grade students (15-16 years of age, 50.2 percent girls) who were enrolled in the Icelandic national education system during February 2012. Through a series of multiple regression models, while controlling for background factors, Attention Deficit Hyperactivity Disorder symptoms and current medication and peer delinquency, and including measures on substance use, the findings show robust additive explanatory power of caffeine for both violent behaviors and conduct disorders. In addition, the association of caffeine to the outcomes is significantly stronger for girls than boys for both violent behaviors and conduct disorders. Future studies are needed to examine to what extent, if at all, these relationships are causal. Indication of causal connections between caffeine consumption and negative outcomes such as those reported here would call into question the acceptability of current policies concerning the availability of caffeine to adolescents and the targeting of adolescence in the marketing of caffeine products. Abstract published by arrangement with Springer.