The use of the internet has become an increasingly integral part of individuals' daily lives, bringing negative consequences such as internet addiction. Understanding the motivations behind internet use is crucial for preventing addiction and developing effective intervention strategies. The objectives of this study are to test the validity and reliability of the Questionnaire of Internet Use Motives (MUI) among Turkish adults and to investigate the predictive effects of socio-demographic variables and internet use motivations on internet addiction. The study was conducted with a sample of 640 adults selected through convenience sampling at two different time points. The majority of participants were women, highly educated, and from a middle socioeconomic background. Data were collected using a socio-demographic questionnaire, the Questionnaire of Internet Use Motives (MUI), and the Internet Addiction Test (IAT). To evaluate the structural validity of the scale, a Confirmatory Factor Analysis (CFA) was performed. Additionally, measurement invariance across genders was examined, and Hierarchical Multiple Linear Regression Analyses were conducted to identify predictors of internet addiction. CFA confirmed the structural validity of the MUI, revealing a five-factor structure with a good fit to the data. The five identified motives were enhancement, coping, social, conformity, and utility. The analyses also demonstrated that the scale possesses convergent and discriminant validity, as well as high reliability. Furthermore, the instrument exhibited measurement invariance across genders. Significant predictors of internet addiction included educational level, socioeconomic status, and the enhancement, social, coping, and conformity motives. The validated MUI provides a robust tool for assessing internet use motives in Turkish adults, offering a foundation for future research and intervention development. Addressing psychological motives such as enhancement, social, coping, and conformity in prevention and treatment strategies may reinforce efforts to mitigate problematic internet use.