The present study reports on the preliminary development and validation of the Youth Internalizing Behavior Screener (YIBS) aimed at assessing internalizing behavior problems in Turkish adolescents. Participants of the study included two independent samples, comprising of 420 adolescents from two public high schools in an urban city of Turkey. Exploratory factor analysis results (N = 217) indicated that the YIBS provided a two-factor latent construct, which comprised of 10 items, with equal items targeting core symptoms of both depression and anxiety disorders. Subsequently, confirmatory factor analysis (N = 203) confirmed the two-factor measurement model and provided good data-model fit statistics. All scales had adequate-to-strong latent construct (H range = 0.84-0.92) and internal reliability estimates ([alpha range = 0.75-to-0.90). Validity analyzes also provided further evidence, demonstrating the small-to-large relationships between the YIBS and criterion variables (e.g., subjective wellbeing, conduct problems, peer problems). Latent variables path model indicated that measurement models had moderate-to-large predictive effects on youth school functioning and wellbeing indicators. Overall, these results suggest that the YIBS may be useful to identify Turkish adolescents with elevated levels of internalizing behavior problems and concurrently poor educational and wellbeing outcomes, providing a warrant for prevention and intervention in school settings.