The primary aim of this study was to investigate the correlation between game addiction and academic achievement. The secondary aim was to adapt a self-report instrument to measure game addiction. Three hundred and seventy high school students participated in this study. Data were collected via an online questionnaire that included a brief explanation of the aim of the study, demographical questions, game addiction scale (GAS) and the grade point average of the current year. The GAS had two forms: (i) 21-item and (ii) 7-item. Game addiction and academic achievement were negatively correlated but this correlation was not supported by regression and structural equation modelling analyses. The present study primarily suggests that there may be a negative correlation between game addiction and academic achievement; however, this correlation may be qualified as negligible. In addition, the two forms of the GAS were adapted for Turkish language with reliability and validity to measure computer and video game addiction in adolescents as promising instruments.