We examined the prevalence of impaired glucose metabolism and its association with inflammation and insulin resistance (IR) in acute myocardial infarction (AMI) patients without a previous diagnosis of diabetes. This prospective study enrolled 52 AMI patients, and 75-g oral glucose tolerance testing was performed on 30 patients at discharge and again 3 months later. We also measured serum adiponectin, high sensitive C-reactive protein, and IL-6 on both occasions. Data were compared with those of 30 type 2 diabetic patients without a history of AMI. Forty percent and 36.7% of AMI patients had impaired glucose tolerance (IGT) at discharge and at 3 months, respectively. The corresponding proportions for newly diagnosed diabetes are 33.0% and 30.0%. At discharge, AMI patients with IGT or diabetes showed higher high sensitive C-reactive protein and IL-6 levels compared with AMI patients with normal glucose tolerance or control type 2 diabetic patients. Furthermore, AMI patients with IGT or diabetes exhibited higher IR and lower serum adiponectin levels than AMI patients with normal glucose tolerance at 3 months after discharge. Previously undiagnosed diabetes and IGT are common in Korean patients with AMI. These glycometabolic abnormalities are associated with inflammation, IR, and serum adiponectin levels.