OBJECTIVE: To examine trends in diabetes prevalence in the U.S. RESEARCH DESIGN AND METHODS: This study was conducted via telephone surveys in states that participated in the Behavioral Risk Factor Surveillance System between 1990 and 1998. The participants consisted of noninstitutionalized adults aged 18 years or older. The main outcome measure was self-reported diabetes. RESULTS: The prevalence of diabetes rose from 4.9% in 1990 to 6.5% in 1998--an increase of 33%. Increases were observed in both sexes, all ages, all ethnic groups, all education levels, and nearly all states. Changes in prevalence varied by state. The prevalence of diabetes was highly correlated with the prevalence of obesity (r = 0.64, P<0.001). CONCLUSIONS: The prevalence of diabetes continues to increase rapidly in the U.S. Because the prevalence of obesity is also rising, diabetes will become even more common. Major efforts are needed to alter these trends.