Diabetes can cause the development of pulmonary complications due to collagen and elastin changes, as well as microangiopathy. This study demonstrates the relationship between pulmonary complications and other chronic complications in diabetes. Twenty-seven patients with diabetes, aged 21 to 62 years, who had had the disease from 3 to 32 years, were included in this study. The protein excretion rate (PER) and the diffusion capacity of the lung for carbon monoxide (DLCO) were included as parameters of the severity of complications. PER was determined by the Biuret method. DLCO was measured by the single-breath method and was corrected by the measurement of alveolar volume (VA). The values of DLCO as corrected by VA (DLCO/VA) were included in the statistical evaluation of the results. The variables of age, duration of diabetes, and complication parameters were included in a multiple regression model with forward, stepwise selection to assess their value in predicting DLCO/VA. The variables were found to be significant predictors of DLCO/VA (R2 = 0.46, adjusted R2 = 0.32, p < 0.022). However, proteinuria was the only significant independent predictor of DLCO/VA. This finding indicates that both renal and pulmonary complications of diabetes share a similar microangiopathic background.