AIM: To evaluate the pulmonary function in patients with type 2 diabetes mellitus in order to identify whether the lung is a target organ of chronic pathologic changes in diabetes mellitus. METHODS: Pulmonary ventilation function and diffusion capacity were studied in 107 patients with type 2 diabetes mellitus and 61 healthy subjects matched for age and sex. Glycosylated hemoglobin (HbA1c), urine albumin excretion rate (AER), fundus examination and nerve conduction velocity were included as parameters of glycemic control and diabetic microangiopathies. RESULTS: Pulmonary ventilation function was similar in type 2 diabetic group and the control. Compared with the control, carbon monoxide diffusion capacity (DLCO) and DLCO corrected by alveolar volume (DLCO/VA) were significantly lower in type 2 diabetic group (P<0.05). DLCO and DLCO/VA were inversely correlated with microangiopathy score (r: -0.291, -0.324, respectively, P<0.01). Furthermore, DLCO/VA was negatively correlated with age and duration of diabetes mellitus (r: -0.269, -0.236, respectively, P<0.05). CONCLUSIONS: Pulmonary ventilation function is normal in patients with type 2 diabetes mellitus, but their diffusion capacity is impaired. It suggests that the lung may also be the target organ of the chronic pathologic changes of diabetes mellitus.