Background: The growing prevalence of being overweight and obesity in children has raised significant public health concerns. Obesity is considered a risk factor for several chronic health conditions and is associated with increased mortality. In addition, recent studies have shown an association between obesity and periodontal disease. Objectives: The present study sought to assess the correlation of body mass index (BMI) with periodontal disease. Materials and Methods: A total of 1,024 12-year-old elementary school students were selected by cluster sampling from five regions of Tehran. BMI was used as a measure of being overweight and obesity, and the oral hygiene index (OHI) was used to assess periodon- tal disease. A linear regression model was applied to estimate the association between BMI and OHI. The parents' level of education and family income were also evaluated. Results: A significant association was found between BMI and OHI (P = 0.001). Also, a significant reverse correlation was detected between the parents' education level with OHI (P < 0.05). Conclusions: Obesity is not a potential risk factor for periodontal disease in children of low-income families. However, periodontal disease is associated with increased BMI. Promotion of healthy nutrition and adequate physical activity may prevent the progression of periodontal disease.