The term prediabetes refers to subjects with impaired fasting glucose and/or impaired glucose tolerance who are at increased risk for type 2 diabetes mellitus. Although both types of patients are at increased risk for developing type 2 diabetes mellitus and cardiovascular disease, they manifest distinct metabolic abnormalities. In this article, we summarize the metabolic abnormalities that characterize each state and the contribution of these metabolic abnormalities to the increased risk of diabetes and cardiovascular disease.