OBJECTIVE Adiponectin has been implicated in the pathogenesis of type 2 diabetes, but its role for incident diabetes, myocardial infarction, or stroke in obesity is unclear. The aim of this study was to analyze the associations between systemic levels of adiponectin and the aforementioned outcomes in a population with severe obesity at high risk of diabetes and cardiovascular events. RESEARCH DESIGN AND METHODS We measured serum concentrations of total adiponectin in 3,299 participants of the prospective controlled Swedish Obese Subjects (SOS) Study (bariatric surgery group, n = 1,570; control group given usual care, n = 1,729). Median follow-up periods ranged between 10 and 13 years for different outcomes. RESULTS In models containing both baseline adiponectin and 2-year changes in adiponectin, high baseline adiponectin and 2-year increases in adiponectin were associated with decreased risk of diabetes and myocardial infarction among controls. In the surgery group, the 2-year weight loss was paralleled by substantial increase in circulating adiponectin (1,807–1,958 ng/mL per 10-kg weight loss). However, neither baseline adiponectin nor 2-year increases in adiponectin were associated with risk of diabetes or myocardial infarction in the fully adjusted models in the surgery group. No associations were found for stroke in either group. CONCLUSIONS Taken together, baseline adiponectin and 2-year changes were associated with incident diabetes and myocardial infarction in the control group but not in the surgery group. Baseline adiponectin did not predict treatment benefit of bariatric surgery.