Impaired glucose tolerance (IGT) is determined by measuring plasma glucose levels 2 hours after glucose loading in the oral glucose tolerance test. There is good evidence from epidemiologic and prospective trials [e.g. Diabetes Epidemiology: Collaborative Analysis of Diagnostic Criteria in Europe (DECODE)] linking IGT with the development of type 2 diabetes mellitus and cardiovascular disease (CVD). IGT is characterized by an increase in postprandial glucose levels, which is considered the earliest metabolic abnormality in type 2 diabetes mellitus. It is one of a series of risk factors for CVD (hypertension, high triglyceride levels, low high-density lipoprotein-cholesterol and central obesity), known as the metabolic syndrome. The different factors making up this syndrome are intimately related. An impaired lipid profile can contribute to insulin resistance, as IGT may play a pathogenic role on other cardiovascular risk factors. IGT is the first easily identifiable step in the pathophysiology of type 2 diabetes mellitus. It is associated with high risk for type 2 diabetes mellitus and subsequent vascular morbidity and mortality. It is currently unknown whether treating IGT will reduce the incidence of macrovascular complications, as studies addressing this issue have yet to be conducted. Therefore, the main reason to identify and treat IGT is to prevent or delay the onset of type 2 diabetes mellitus. It has been demonstrated that lifestyle intervention with diet and exercise can reduce the incidence of type 2 diabetes mellitus. Pharmacologic intervention with metformin and acarbose is also effective. Other drugs, such as those indicated to treat other parameters of the metabolic syndrome, may also be useful. We can now be assured that prevention or delay of onset of type 2 diabetes mellitus is possible in individuals with IGT, either by changes in lifestyle or by pharmacotherapy.