Objective: The relationship between screen use and problematic internet use (PIU; i.e., internet addiction) amongst adolescents has not been sufficiently explored. Further, there is even less research on how gender is associated with this relationship. The goal of the study was to examine adolescent screen use, PIU, and its impact on day-to-day routines of adolescents. Methods: Participants were recruited from an outpatient pediatric clinic in São Paulo, Brazil. A total of 180 adolescents completed questionnaires related to their screen use, extracurricular activities, and symptoms of PIU. Univariate and multivariate statistics were used to determine correlates and predictors of PIU, and to explore gender differences. Results: A total of 26.1% of adolescents met the criteria for PIU. There were no significant differences between boys and girls in PIU severity. However, there were significant gender differences in preferred use of the Internet, with boys being more likely to access the Internet to play video games (odds ratio [OR]=27.1) and girls being more likely to socialize with friends (OR=4.51). PIU severity increased proportionally to the number of hours of use of all screen devices with moderate-to-large effect sizes (η2=0.060–0.157). Using screens during meals and missing extracurricular activities were both associated with PIU. Conclusion Though gender was not associated with PIU, both excessive use of screen devices during meals and neglect of offline extracurriculars activities were identified as risk factors for PIU. Prevention measures should consider the impact of gender and associated patterns of motivation and Internet use.