OBJECTIVE - To determine the age- and sex-specific prevalence of impaired fasting glycemia, impaired glucose tolerance, screen-detected diabetes, and known diabetes in a Danish population aged 30-60 years and to examine the phenotype and the cardiovascular risk profile in individuals with impaired glucose regulation. RESEARCH DESIGN AND METHODS - In the Inter99 study, 13,016 inhabitants living in Copenhagen County were invited. All participants underwent anthropometric measurements, blood samples, and a 75-g standardized oral glucose tolerance test. RESULTS - The age-specific prevalences in men were as follows: impaired fasting glycemia: 1.4-16.3%; impaired glucose tolerance: 6.9-17.8%; screen-detected diabetes: 0.7-9.7%; and known diabetes: 0-5.8%. The corresponding figures in women were 0-5.1, 10.5-17.3, 0.6-6.3, and 0.5-9%. The prevalence of impaired glucose regulation increased with age. Among individuals with diabetes, 65.6% were previously undiagnosed; this proportion was highest in the youngest age-group (82% among 45-year-old men vs. 63% among 60-year-old men, and 70% among 45-year-old women vs. 52% among 60-year-old women). Mean BMI, waist, HbA1c, systolic blood pressure, diastolic blood pressure, and total cholesterol were significantly higher (P < 0.0001) in the individuals with impaired glucose regulation compared with individuals with normal glucose tolerance. CONCLUSIONS - This study revealed that the prevalence of type 2 diabetes is high and that still two out of three individuals are undiagnosed, indicating a need for more attention to the disease in society.