Objectives: The aim of this study was to estimate the prevalence of diabetes, impaired glucose tolerance (IGT), and impaired fasting glucose (IFG) in first-degree relatives (FDR) of people with type 2 diabetes mellitus. Methods: A cross-sectional study of FDR of type 2 diabetes patients was conducted between 2003 and 2005. A total of 2,368 FDR of type 2 diabetes outpatients aged 30-60 years (614 men and 1754 women) from Isfahan Endocrine and Metabolism Research Center (Iran) were examined. All subjects underwent a standard 75 g 2-h oral glucose tolerance test (OGTT). IGT, IFG and type 2 diabetes were diagnosed according to the criteria of the American Diabetes Association (ADA). The mean (SD) age of participants was 43.1 (6.9) years. Results: The prevalence of type 2 diabetes, IGT and IFG were 10.3% (95% CI: 9.1-11.5), 19.5% (17.9-21.1) and 17.3% (15.8-18.8) respectively. The prevalence rates were significantly higher than those reported for a control population of the same age (type 2 diabetes, 6.0% (95% CI: 5.7-6.2) and IGT 9.6 (95% CI: 9.3-9.9)). IGT was more frequent among women (OR: 0.66; 95% CI: 0.51-0.87), whereas diabetes (OR: 1.31; 95% CI: 0.96-1.78) and IFG (OR: 1.41; 95% CI: 1.10-1.80) were higher in men. Multivariate analysis revealed that age and obesity or abdominal obesity were significantly associated with diabetes, IGT and IFG. Conclusion: FDR of people with type 2 diabetes in Iran are at higher risk of IGT and type 2 diabetes than the population at large. Risk increases with age and obesity. These findings may be useful for the identification of persons at risk of developing type 2 diabetes and strongly support the regular screening of FDR of type 2 diabetes patients.