OBJECTIVE: Although clinically evident type 2 diabetes is a well-established cause of mortality, less is known about subclinical states of glucose intolerance. RESEARCH DESIGN AND METHODS: Data from the Second National Health and Nutrition Examination Survey Mortality Study, a prospective study of adults, were analyzed. This analysis focused on a nationally representative sample of 3,174 adults aged 30-75 years who underwent an oral glucose tolerance test at baseline (1976-1980) and who were followed up for death through 1992. RESULTS: Using 1985 World Health Organization criteria, adults were classified as having previously diagnosed diabetes (n = 248), undiagnosed diabetes (n = 183), impaired glucose tolerance (IGT) (n = 480), or normal glucose tolerance (n = 2,263). For these groups, cumulative all-cause mortality through age 70 was 41, 34, 27, and 20%, respectively (P < 0.001). Compared with those with normal glucose tolerance, the multivariate adjusted RR of all-cause mortality was greatest for adults with diagnosed diabetes (RR 2.11, 95% CI 1.56-2.84), followed by those with undiagnosed diabetes (1.77, 1.13-2.75) and those with IGT (1.42, 1.08-1.87; P < 0.001). A similar pattern of risk was observed for cardiovascular disease mortality. CONCLUSIONS: In the U.S., there was a gradient of mortality associated with abnormal glucose tolerance ranging from a 40% greater risk in adults with IGT to a 110% greater risk in adults with clinically evident diabetes. These associations were independent of established cardiovascular disease risk factors.