The aim of this study was to investigate the association between sleep duration, overweight/obesity, and school failure using data obtained from self-reported questionnaires completed by 13- to 15-year-olds in Sweden (n = 1,363; 50.7% female). The height and weight of the participants were measured by school nurses. A multiple logistic regression analysis was used to analyze the association between sleep duration and overweight/obesity, school failure, and perceived economic situation. A short sleep duration (<7 hr) was associated with overweight/obesity (p = 0.001), school failure (p = 0.007), and poorer perceived economic situation (p = 0.004). Modifying the sleep habits of adolescents is a potential target for obesity intervention as well as for improving school success. This information is particularly well suited for school nurses to disseminate to students and their parents.