Objective: To evaluate the relationship between waist circumference, as a measure of central fat distribution, and lung ventilation function in both sexes among different weight categories in comparison with body mass index (BMI). Subjects and Methods: One hundred healthy adults from both sexes were volunteered in this observational-cross-sectional study (53 males aged 19-69 years and 47 females aged 19-51 years). Subjects were recruited from Mosul Medical College students, teaching as well as administration staff. After collecting personal and health information necessary for the study, all subjects underwent anthropometric measurements (height, weight, and waist circumference) before spirometry test using computerized spirometer. The study was conducted in the Department of Medical Physiology-Mosul Medical College. Results: All spirometric data were within 80-120% of the normal predicted values, thus excluding the possibility of any asymptomatic airway disease. A consistent negative correlation between, both waist circumference and BMI, with FVC and FEV1 were clearly observed in both sexes. Unlike BMI, waist circumference revealed stronger and significant negative correlation with lung function especially in male subjects. The significant negative correlation between waist circumference and FVC and FEV1 was more evident in overweight and obese subjects. Conclusion: Waist circumference, as a measure of body fat distribution, seems more reliable predictor of poor lung function, secondary to overweight and obesity, than BMI. This might be attributed to the fact that BMI relies only on body weight and height without consideration to the distribution of body fat, muscle and bone mass which might possess a more significant role.