Background: The prevalence of both obesity and asthma has risen in recent years. We sought to investigate whether obesity may be related to asthma. Materials and methods: In this analytical study, 177 patients with asthma were enrolled. Obesity was defined as a body mass index (BMI) greater than 30. Asthma severity was defined by using the National Heart Lung and Blood Institute 1997 guidelines. Results: Of the 177 patients, there were 80 males and 97 females. 38.4 percent of the sample was obese. There is no significant relationship between BMI and asthma severity (P=0.76) but as established by Pearsons correlation coefficient a positive and significant correlation is present between BMI and FEV1/FVC values (r=0.32 P=0.0001). Females with asthma were significantly more overweight than males (p = 0.001). Conclusions: In our study, there was a significant correlation between body mass index and sex of patients with asthma. Women had the highest percentages of asthma compared to men, and had a higher body mass index than men.