The criteria of the American Diabetes Association and the WHO for the diagnosis of diabetes mellitus are controversially discussed. In a prospective population study, we evaluated the data of 3,737 men, aged 36-60 yr, without diabetes mellitus and with fasting serum glucose levels less than 7 mmol/L at entry into the study who had at least 1 repeat examination during a follow-up of 4-10 yr. During a mean follow-up of 6.3 yr, 200 men developed diabetes mellitus. They differed significantly from 3,537 men by body mass index, fasting serum levels of glucose, high density lipoprotein cholesterol, and family history positive for diabetes mellitus. Receiver operating curve analysis revealed that a glucose level of 5.72 mmol/L was the best discriminatory cut-off. Upon global risk estimation by multiple logistic function (MLF) analysis, 69.6% of all diabetes mellitus incidences occurred in the highest quintile as defined by the MLF algorithm. The relative risk of a men in this quintile was 8.7 compared to that in the residual population. The performance of risk assessment by MLF as estimated by the area under the receiver operator characteristic curve was similar to fasting glucose levels. Global risk estimation by multiple risk factors does not improve the prediction of diabetes mellitus by fasting glucose in middle-aged men. The lower discriminatory cut-off of 5.72 mmol/L glucose may help to reduce the previously reported discordance between impaired fasting glucose (American Diabetes Association) and impaired glucose tolerance (WHO) in diagnosis of the prediabetic state.