A cross-sectional study was undertaken to assess the co-relation of BMI with the prevalence and severity of asthma in 23 school children aged 9.13 2.20 and the BMI of 16.27 3.11. Automated spirometer was used to assess the lung function tests of the children. We used mainly PEF as a guideline to make the diagnosis of asthmatic or non-asthmatic based on the spirometric results. Reversibility of airway obstruction was done by repeating spirometry after two puffs of salbutamol inhaler. The results indicate that BMI, which is a measure of body fat, has a strong co-relation with the lung function tests. A significant decrease was observed in the values of Pre-PEFR and FEV1 with an increasing BMI indicating that body fat has a bearing on the severity of asthma (p=0.001). No significant relationship was identified between % FEV1 and BMI. Per-PEFR showed a trend towards becoming significant (p=0.187). This study supports the view that there is a definite trend co-relating severity of asthma symptoms and body weight.