Objective: A retrospective study was performed to evaluate the effect of body mass index (BMI) on the clinical course of appendicitis in children. Material and Methods: Patients between 6 and 18 years of age, who had undergone appendectomy in the last 2 years, were evaluated for age, sex, BMI, time from the beginning of complaints to diagnosis, acute Or perforated appendicitis, duration of hospitalization and complications retrospectively. BMI was evaluated according to percentiles developed for Turkish children between 6 and 18 years of age. Patients with percentiles between 10 to 75 were accepted as the normal BMI group, lower than 10 was the low BMI group and more than 75 was assessed as the high BMI group. Results: Ninety-six patients were included in the study. The median age was 13 (min: 6, max:16) in the normal BMI group [n=37, male/female (M/F)=1.84], 12(6-16) in the low BMI group (n=38, M/F=1.53) and 9(6-15) in the high BMI group (n=21, M/F=3.2). The acute/perforated appendicitis ratios were 3.1, 2.8 and 1.3, respectively in the normal, low and high BMI groups. There was no significant difference between the groups regarding the time from the beginning of complaints to diagnosis and duration of hospitalization (p>0.05). Although complication rates showed no difference between the normal and low BMI groups, the high BMI group had a higher incidence of complications compared to the normal and low BMI groups (p=0.04 and p=0.018,respectively). The follow-up period of the patients were 2 months to 2 years and the most common complication was wound infection. Conclusion: Children with high BMI have higher complication rates during the clinical course of appendicitis compared to children with low and normal BMI.