The aim of this study is to investigate the predictive effects of internet addiction on happiness for the adolescents who study in sports high school. The study was conducted with 135 high school students, 68 females and 67 males. For the data collection tool in the study, Young’s Internet Addiction Test-Short Form, Oxford Happiness Questionnaire-Short Form and the personal information form prepared by the researcher were adopted. The data analyses were conducted using the Pearson Product-Moment Correlation Coefficient and Simple Linear Regression analyses. As a result of the analyses, statistically significant and negative relationships were found between the internet addiction and the happiness levels of students of sports high school. As a result of the regression analysis, it was revealed that the internet addiction of the students of sports high school significantly predicted happiness in a negative way. According to the results of the study, it could be stated that internet addiction could affect happiness negatively. It is believed that the results obtained are of significance in terms of detecting the effects of internet use on adolescents who study in sports high school and in offering an insight for future studies. The results were discussed within the framework of the literature and various suggestions were offered.