Background: Chronic hyperglycaemia causes many changes in the lungs such as thickened pulmonary capillary basal lamina and alveolar epithelium causing decreased pulmonary elastic recoil and lung volumes. Aim: of the current study is to know the evidence based signicance of spirometry on type 2 diabetes mellitus. Methods: This was a cross sectional observational study with 90 Type 2DM patients were selected of age more than 35 years and with duration of diabetes > 5 years. spirometry was done for: FVC, FEV1, FEV1/ FVC. Results: Recorded FVC in Type 2 DM is decreased when compared to the predicted values.Recorded FVC of diabetic patients have a mean of 2.14 ± 0.67 with a range of 1.13 – 4.17 compared to predicted values with mean of 2.54 ± 0.63 with a range of 1.72 – 4.03. Recorded FEV1 in Type 2 DM is decreased when compared to the predicted values. Recorded FEV1 of diabetic patients have a mean of 1.93± 0.63 with a range of 0.95 – 3.33 compared to predicted values with mean of 2.10 ± 0.49 with a range of 1.42 – 3.36. 53.3% of the diabetics had mild restriction of pulmonary functions 14.4% of the diabetics had moderate restriction of pulmonary functions. Conclusion: DIABETES MELLITUS causes decrement in the lung functions in the form of Restriction which is more seen in patients with longer duration of DM & patients with uncontrolled glycemic status.