Much is known about the influence of potential lifestyle factors on adolescents' nutritional status, but in Croatia there are not many studies of this topic. Past studies have shown many variables associated with being overweight/obese. Thus, this study investigated the associations between the overweight/obesity status and lifestyle factors of Croatian adolescents. In this cross-sectional study, participants were 1,950 urban secondary-school students (884 male, 1,066 female) aged 17 to 18 years old. The dependent variable was body mass index derived from self-reported height and weight. The outcome was binarized, where participants with value < 25.0 lb/in were collapsed into normal weight, while those = 25.1 lb/in into the overweight/obesity weight category. Independent variables were gender, type of school, physical activity, sedentary behavior, self-rated health, self-perceived socioeconomic status, and psychological distress. The associations between the dependent and independent variables were analyzed through multiple logistic regression analysis. In the univariate model, being overweight/ obese was significantly associated with a male gender (OR 0.31; 95% CI 0.23 to 0.42), attending a vocational school (OR 1.87; 95% CI 1.42 to 2.48), not meeting the recommendations for moderate-to-vigorous physical activity (OR 0.44; 95% CI 0.22 to 0.88), more time spent in sedentary behavior (OR 1.53; 95% CI 1.07 to 2.19), poor self-rated health (OR 0.35; 95% CI 0.20 to 0.56), and lower socioeconomic status (OR 0.63; 95% CI 0.48 to 0.84). In the multivariate model, the same associations occurred between the dependent and independent variable. In both models, psychological distress was not associated with being overweight/obese. In conclusion, the findings suggest that lifestyle factors are independently associated with body mass index.