The severity of bronchial asthma is determined by the frequency, duration and intensity of asthmatic attacks, activity and symptoms outside attacks and pulmonary function. Many factors including age, sex, anthropometric indices and race affect lung function parameters. Poor asthma control may also affect lung function indices of asthmatics. However, relatively little is known about the extent to which asthma duration affects lung function parameters of asthmatics in our environment. This aim of this study was to clarify the relationship between the duration of asthma and lung function parameters among patients with mild to moderate bronchial asthma in our setting. Methods: Patients with asthma were classed into two groups; Long Duration of Asthma (LDA) with a clinical course of more than 10 years and Short Duration of Asthma (SDA) with a clinical course of 10 years or less. Lung function parameters were carried out according to the American Thoracic Society guidelines. Results: The median duration of asthma for all the subjects was 10 (1-43).There was a statistically significant difference in the duration of asthma between the two groups, LDA group median duration of asthma was 18 (10-43) compared to SDA group of 2.5 (I-I0) (P