The target organs in diabetes mellitus include the kidneys, the eyes and the small vessels. In these organs some specific histopathological changes have been described but there are few reports of histopathoogical changes in the lung in diabetic patients. Several reports describe abnormal pulmonary function in diabetic patients and consider these abnormalities to be due to histopahtological changes found in the pulmonary vessels. We have studied the histopathological changes in the diabetic lung comparing the findings in the autopsies of 61 diabetic and 50 non-diabetic patients. Statistically significant differences in the incidence of chronic obstructive lung disease and pulmonary haemorrhage exist. There are no differences in the incidence of fibrosis of the alveolar walls or intimal and medial thickening of small vessels, changes associated with diabetes according to the literature. We have found a specific type of nodular fibrosis not previously reported which we believe to be typical of diabetes.