Objective: Problematic internet use and poor sleep quality are widespread problems in adolescents. The aim of this study is to investigate the relationship between problematic internet use, sleep quality and impulsivity in adoles-cents diagnosed with major depressive disorder and to compare the findings with those of healthy controls. Meth-ods: The study was planned as a single-disciplinary, three-centered, cross-sectional study with a control group. All participants were assessed using the Kiddie Schedule for Affective Disorders and Schizophrenia Present and Life-time Version (K-SADS-PL). Beck Depression Inventory (BDI), Barratt Impulsiveness Scale (BIS-11), Pittsburgh Sleep Quality Index (PSQI) and Youngs Internet Addiction Test (IAT) were administered to all participants. Results: It was determined that the total scores of BIS-11 scale, PSQI and IAT were statistically and significantly higher in the depression group than controls. In addition, a positive correlation was found between IAT and BIS-11 score and between IAT and PSQI. A positive correlation was also found between BIS-11 and PSQI. Conclusion: According to the findings of our study, it is suggested that there may be multiple and complex interactions between problematic internet use, low sleep quality, impulsivity and depressive symptoms. [Anadolu Psikiyatri Derg 2019; 20(5.000): 491-498]