Diabetes mellitus (DM) is a common endocrinopathy of cats and humans. Although few studies have examined the effects of DM on the pulmonary system, changes in pulmonary function and immunology in humans with type I and II diabetes, and pulmonary lesions in a murine diabetic model have been documented. Our objective was to determine whether pulmonary lesions occurred in cats with DM. Medical records and necropsy evaluations of 42 cats with DM were compared with those of 45 age-matched, nondiabetic cats for the presence of clinical evidence of respiratory disease and pulmonary histopathological findings at the time of necropsy. No statistical difference was noted in the presence of clinical evidence of respiratory disease between cats with diabetes and control cats. Nevertheless, there was a significant association between the presence of abnormal pulmonary histopathology and DM (P = .018, odds ratio = 3 inclusive of all cats; P = .005, odds ratio = 5 when non-DM cats with overt clinical evidence of respiratory disease were excluded). Pulmonary abnormalities detected by histopathological examination in cats with diabetes included congestion and edema, histiocytosis, pneumonia, smooth muscle hypertrophy, fibrosis, mineralization, neoplasia, and type II pneumocyte hyperplasia. The observed association between DM and pulmonary lesions in cats, independent of clinical evidence of respiratory disease, emphasizes the need for careful assessment of the respiratory tract in sick cats with diabetes.