At least one fourth of U.S. adults are known to have prediabetes, a condition defined as having impaired fasting glucose (plasma glucose level of 100 to <126 mg/dL after an overnight fast), impaired glucose tolerance (plasma glucose level of 140 to <200 mg/dL after a 2-hour oral glucose tolerance test), or both. Persons with prediabetes are at increased risk for developing type 2 diabetes, heart disease, and stroke. However, lifestyle changes can prevent or delay development of diabetes and its complications among persons with prediabetes. To assess the prevalence of self-reported prediabetes among U.S. adults and the prevalence of activities that can reduce the risk for diabetes, CDC analyzed responses to questions regarding prediabetes asked for the first time in the 2006 National Health Interview Survey. This report summarizes the results of that analysis, which determined that, although at least one fourth of U.S. adults are known to have prediabetes through surveys that included laboratory testing, in 2006, only an estimated 4% of U.S. adults had been told they had prediabetes. Among those who had been told they had prediabetes, 68% had tried to lose or control weight, 55% had increased physical activity or exercise, 60% had reduced dietary fat or calories, and 42% had engaged in all three activities. Persons at greater risk for diabetes should be tested according to published recommendations, and persons with prediabetes should lose or control their weight and increase their physical activity to reduce their risk for developing diabetes.