The aims of the study were to assess prevalence and gender differences of addictive behaviors (substance- and non-substance-related) in an adolescent population, and their association with psychopathological features and academic performance. A sample of high school Italian students (n = 996; M = 240, F = 756) was examined using a self-report survey concerning sociodemographic characteristics, cigarette smoking, alcohol and substance use, perceived academic performance, activities, and behaviors (Internet use, gambling, and physical exercising). The Internet Addiction Test, the South Oaks Gambling Screen-revised Adolescent, and the Exercise Addiction Inventory-Short Form were administered to identify problematic behaviors. The Barratt Impulsiveness Scale for Adolescent, the Snaith-Hamilton Pleasure Scale, the Dissociative Experience Scale for Adolescent, and the Toronto Alexithymia Scale were used to investigate psychopathological dimensions. Frequent alcohol intake and lifetime substances consumption were more common among males. The occurrence of other addictive behaviors was 22.1% for problematic Internet use (M = F), 9.7% for at-risk/problematic gambling (M > F), and 6.2% for maladaptive physical exercise (M = F). We also found an association between substance-/non-substance-related addictive behaviors and psychopathological dimensions. Addictive behaviors were more frequent among students reporting poor school performance. Our study showed a relevant prevalence of addictive behaviors in a sample of Italian high school students, with specific gender differences. We underlined the cooccurrence of substance and non-substance-related addictive behaviors, and their association with worse school performance. Dissociative proneness, anhedonia, alexithymia, and impulsivity were associated with addictive behaviors in adolescents and might represent vulnerability factors for the development of psychiatric disorders in adulthood. A better understanding of psychopathological features associated with addictive behaviors might be useful for the prevention/early intervention.