OBJECTIVE: Adiponectin is an adipose tissue-derived protein. Low levels are associated with obesity, insulin resistance, and type 2 diabetes. Our objective was to investigate the prospective association between adiponectin levels and the 6.4-year risk of type 2 diabetes and of impaired glucose metabolism (IGM). RESEARCH DESIGN AND METHODS: The Hoorn Study is a cohort study among Caucasians, aged 50-75 years. BMI, waist-to-hip ratio (WHR), fasting glucose, 2-h glucose, triglycerides, HDL cholesterol, LDL cholesterol, alanine aminotransferase, leptin, and adiponectin were measured at baseline. Lifestyle (alcohol intake, smoking, and physical activity) was assessed by questionnaires. After a mean follow-up of 6.4 years, glucose tolerance was assessed by a 75-g oral glucose tolerance test. Analyses were performed in 1,264 subjects (584 men and 680 women) without type 2 diabetes at baseline. For analyses of incident IGM, 239 subjects with IGM at baseline and/or type 2 diabetes at follow-up were excluded. RESULTS: Age- and lifestyle-adjusted odds ratios and 95% CIs comparing highest with lowest adiponectin quartile were 0.52 (0.23-1.18) in men and 0.15 (0.06-0.39) in women for type 2 diabetes and 0.90 (0.51-1.61) and 0.28 (0.16-0.48) for IGM, respectively. The risks were only slightly reduced after adjustment for WHR and leptin as markers of (abdominal) adiposity. Adjustment for baseline fasting and postload glucose levels (potential mediators) substantially diminished these inverse associations with type 2 diabetes (0.79 [0.32-1.91] and 0.62 [0.21-1.81]) and with IGM (1.20 [0.61-2.35] and 0.48 [0.26-0.90]), respectively. CONCLUSIONS: A high adiponectin level was strongly associated with a lower risk of IGM and type 2 diabetes, particularly in women. These results suggest that adiponectin is involved in the pathophysiology linking obesity to type 2 diabetes.