Statement of the Problem: The prevalence of overweight and obesity has been increasing markedly in recent years. It may influence growth in pre pubertal children.Purpose: The purpose of this study was to determine whether increased Body Mass Index (BMI) is associated with accelerated skeletal maturation and dental maturation in six to fifteen years old orthodontic patients in Shiraz, Iran.Materials and Method: Skeletal maturation and dental development of 95 orthodontic patients (65 females and 30 males), aged 6 to 15 years, were determined. Dental development was assessed using the Demerjian method and skeletal maturation was evaluated by cervical vertebral method as presented by Bacetti. The BMI was determined for each patient. T-test was applied to compare the mean difference between chronologic and dental age among the study groups. A regression model was used to assess the relationship between BMI percentile, skeletal maturation, and dental development.Results: 18.9% of subjects were overweight and obese. The mean differences between dental age and chronologic age were 0.73±1.3 for underweight and normal weight children and 1.8±1.08 for overweight and obese children. These results highlighted the correlation between accelerated dental maturity and increasing BMI percentile (p= 0.002). A new formula was introduced for this relationship. There was not any significant relationship between BMI percentile and skeletal maturation.Conclusion: Children who were overweight or obese had accelerated dental development whereas they did not have accelerated skeletal maturation significantly after being adjusted for age and gender.