OBJECTIVE The American Diabetes Association (ADA) has recommended that the fasting plasma glucose (FPG) level used to diagnose diabetes be changed from 7.8 mmol/l (the level recommended by the National Diabetes Data Group [NDDG] in 1979) to 7.0 mmol/l. We examined the impact of this change on rates of progression to overt diabetes from different levels of FPG. RESEARCH DESIGN AND METHODS Using the laboratory database of Mayo Clinic, we assembled a cohort of 8,098 nondiabetic Olmsted County residents 40 years of age or older on 1 July 1983. Subjects were followed for a median of 9 years. RESULTS Among 7,567 individuals with follow-up FPG data, 778 (10.3%) progressed to ADA diabetes and 513 (6.8%; P < 0.0001) progressed to NDDG diabetes. The risk of developing ADA diabetes was 7, 19, and 39% for individuals with initial FPG values in the ranges of <5.6, 5.6–6.0, and 6.1–6.9 mmol/l, respectively. For progression to NDDG diabetes, the respective risks were 3, 11, and 25%. A clear gradient of risk was observed within the “normal” range of FPG (<5.6 mmol/l). Among the 793 individuals who developed ADA diabetes, 222 (29%) developed NDDG diabetes simultaneously and 291 (37%) developed NDDG diabetes later. In all FPG subgroups, progression to ADA diabetes occurred ∼7 years sooner than progression to NDDG diabetes. CONCLUSIONS The baseline level of FPG is a major predictor of an individual9s risk of developing diabetes. The proposed change in the diagnostic criteria for diabetes will lead to earlier diagnosis among individuals who are destined to develop the disease.