Background/Aim: Obesity in adolescents is increasing; as such, the aim of this study was to determine the prevalence of obesity in Mexican adolescents and examine its possible association with hours of sleep. Methods: A school-based cross-sectional study was carried out. This study included 863 adolescents aged between 11 and 16 years. The prevalence of obesity was estimated using the body mass index (BMI). The duration of sleep (and other information) was assessed by a self-reported questionnaire. The Cochran–Mantel–Hansel test for categorical variables and a general linear model for continuous variables were used to evaluate the interaction effect of BMI and sex with respect to sleeping and assessed activity conditions. Results: It was found that 47.6% of the adolescents were overweight/obese. Men were more frequently overweight/obese than women (52.6% vs. 41.8%, p = 0.002). Moreover, overweight/obese adolescents were younger and spent fewer daily hours watching television (p < 0.05). Men practiced sports more hours per week than women (p = 0.04). However, women spent more daily time on the internet (p = 0.05), and overweight/obese adolescent women slept fewer hours than overweight/obese men and adolescents with normal weight (p = 0.008). Conclusions: The development of strategies for the prevention of overweight/obesity and the improvement of sleep duration should include a gender perspective to improve health habits in Mexican adolescents.