OBJECTIVE- The aim of this study was to test the hypothesis that diabetes is independently associated with reduced lung function, both cross-sectionally and longitudinally. RESEARCH DESIGN AND METHODS - We conducted cross-sectional and prospective analyses of diabetes status and lung function decline using baseline and 3-year follow-up data on 1,100 diabetic and 10,162 nondiabetic middle-aged adults from the Atherosclerosis Risk in Communities (ARIC) Study. Forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV 1) were measured at baseline and at the 3-year follow-up using standard spirometry. RESULTS - At baseline, adults with diabetes had significantly lower predicted FVC (96 vs. 103%, P < 0.001) and predicted FEV 1 (92 vs. 96%, P < 0.001) than those without diabetes. These differences remained significant after adjustment for demographic characteristics, adiposity, smoking, physical activity index, education, and ARIC field center. Graded, inverse associations were observed between hyperglycemia, diabetes severity (i.e., duration of diabetes and types of antidiabetes medications), and FVC and FEV 1 (all P trend < 0.001). In prospective analyses, FVC declined faster in diabetic adults than in their nondiabetic counterparts (64 vs. 58 ml/year, P = 0.01). Diabetes severity as indicated by intensity of antidiabetic treatment also showed graded relationships with the rate of FVC decline (P < 0.01). CONCLUSIONS - These data support the notion that the lung is a target organ for diabetic injury. Additional research is required to identify pathophysiologic mechanisms and to determine clinical significance.