ABSTRACT:The study involved 100 patients who presented at Department of pulmonary medicine, Alluri sitaramaraju academy of medical sciences, Eluru between December 2011 and December 2012. Also 100 normal persons were taken in to the study to compare the normal ventilatory function with the standards. There was a male preponderance in the study, about 75% of the study group were males. The mean height of males in the control group was 164.12±8.6 and 152±5.8 cm for females. The mean height (cm) of males in the cases was 162±9.2 and that of females is 149.6±4.6. (Mean±SD). The mean age (Years) of smokers in males was 49.05±12.2. The ratio of smokers to non-smokers with the study group was 3:2 while that of control group was 2:3. In both the groups, the smokers were moderate to heavy smokers. Most of the subjects in control group had 75% or above of the standard values for all the parameters studied-FVC, FEV1, FEV1/FVC%. Restrictive ventilatory defect was the most commonly observed ventilatory defect in our study. It was assosciated with most of the diseases studied-pneumonias, mass lesions of the lung, fibrocavities, pleural lesions. Obstructive ventilatory defect was prevalent among asthma and COPD as they are obstructive lung diseases. A mixed ventilatory defect was also seen in this group. Mixed ventilatory defect was seen in most of the post tubercular lesions of the lung-fibrosis, bronchiectasis and mass lesions of the lung. Grading of the severity of disease was done based on international accepted criteria like GINA, GOLD etc. Severity of the ventilatory defect correlated with the severity of various diseases. Some of the patients had normal ventilatory function even in the presence of the disease as the lung has a very large respiratory reserve. Mean FVC, FEV1 are predominant in males when compared to females in both controls and cases. This may be attributed to the well-built and nourishment among males. The ventilator function parameters (Mean FVC, FEV1) were significantly low in cases in comparision to controls. It may be due to the effect of respiratory illness. FEV1% predicted was significantly decreased in obstructive ventilatory defect in cases when compared to controls in both males and females. Spirometry is useful tool in evaluating ventilator function abnormalities in various pulmonary diseases and assessing their severity. This information is useful in management of patients, monitoring and for long term follow up. It helps to understand the physiologic working of lungs and chest mechanics.