Objective: To evaluate the prevalence of genu valgum and associated factors in elementary school students. Methods: Cross-sectional study, carried out in 2015, with 1,050 children and adolescents enrolled in an elementary school in Santos, Southeast Brazil. Misalignment of the knee was assessed by intermalleolar distance, considering ≥8 cm or <8 cm. Inter-examiners reliability was measured by Kappa coefficient, resulting in 0.94. Nutritional status was evaluated according to the World Health Organization 2006 references. Logistic regression model was applied to analyze variables associated with genu valgum. Results: Among schoolchildren, 7.1% had genu valgum. The frequency was higher among overweight or obese schoolchildren. On average, students with genu valgum are older than those without it. There was no association with gender. Upon logistic regression model, only nutritional status was significantly associated with this condition. The chance of occurrence of valgus knee in overweight and obese schoolchildren was, respectively, 6.0 and 75.7 times greater than among thin or eutrophic subjects.Conclusions: The prevalence of genu valgum in elementary school children and adolescents was 7.1%, being higher among overweight/obese students and presenting no association with gender or age.