Objective: Although obesity was found to be associated with severe impairment of ventilation, most of the study population has been morbidly obese adults. We aimed to explore the effects of mild obesity on ventilatory function in the pediatric age group. Methods: In a cross-sectional controlled study, 80 patients (M/F: 35/45), who were evaluated in our outpatient clinic with the complaint of excess body weight, with no history of asthma or other atopic diseases were studied and compared to a control group of 50 normal weight children controlled for age and sex. The mean age of patients was 9.7±2.5 years (7 to 15 years). Anthropometric measurements and spirometry were performed in all subjects. Forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) were used as measures of ventilatory function. Results: There were no significant differences in FEV1%, FVC% and FEV1%/FVC% by study group (p > 0.05). Only three patients had obstructive abnormalities documented on their pulmonary function tests (two had moderately severe and one had mild obstructive abnormalities). No correlation was observed between pulmonary function parameters and anthropometric measurements. Conclusion: These data demonstrate that pulmonary function test parameters of the mildly obese children were similar to those of the normal weight children. Anthropometric measurements had no significant effect on spirometric measurements in children as they did on adults. Copyright © 2007 by Sociedade Brasileira de Pediatria.