Background: Environmental factors may affect adolescents' eating habits and thereby body weight. However, the contribution of school neighbourhood environment is poorly understood. This study examined the association between proximity of a fast-food outlet or grocery store to school and adolescents' eating habits and overweight. Methods: Participants were 23 182 adolescents (mean age 15 years) who responded to a classroom survey in 181 lower secondary schools in Finland (2008-09). School location was linked to data on distance from school to the nearest fast-food outlet or grocery store (<= 100 m, 101-500 m, >500 m) using global positioning system-coordinate databases. Outcomes were irregular eating habits (skipping breakfast, skipping free school lunch, skipping free school-provided snacks and not having family dinners), the accumulation of these habits and overweight, including obesity (body mass index >= 25 kg/m(2)). Results: Thirteen percentage of the participants were overweight. Having a fast-food outlet or grocery store near school was associated with skipping often breakfast and free school lunch, and the accumulation of irregular eating habits. The proximity of a fast-food outlet or grocery store was associated with a 1.25-fold (95% confidence interval 1.03-1.52) risk of overweight among adolescent with a low socioeconomic status but not among those with higher socioeconomic status. This association was partly (12%) explained by the accumulation of irregular eating habits. Conclusions: Among adolescents from low socioeconomic background, the presence of fast-food retailers near schools is associated with accumulation of irregular eating habits and greater overweight. These findings suggest that obesogenic school neighbourhoods may contribute to social inequalities in overweight.