Racial origin and family history of type 2 diabetes impact upon the risk of developing impaired glucose tolerance (IGT) and type 2 diabetes, both of which are common in women with polycystic ovary syndrome (PCOS). We examined the effects of race and family history of type 2 diabetes on the risk of IGT and type 2 diabetes in a large cohort of women with PCOS. Data obtained at baseline were analyzed from 408 premenopausal women with PCOS. Multivariate linear regression models were used to assess the impact of race (white, black, and other) and family history of type 2 diabetes on body mass index, waist circumference, and waist to hip ratio; glycemic measures (glucose and insulin levels obtained during a standard 75-g oral glucose tolerance test, fasting glucose to insulin ratio, and homeostasis model assessment model of insulin resistance derived from fasting levels of glucose and insulin), hemoglobin A(1c), and SHBG, and dehydroepiandrosterone sulfate levels. Sixteen (4%) of the 408 patients had type 2 diabetes, 94 (23%) had IGT, and the remaining 298 (73%) had normal glucose tolerance. A history of type 2 diabetes in either parent (FHxPOS) was present in seven (44%) of the 16 diabetic women with PCOS, 37 (39%) of the 94 women with IGT, and 62 (21%) of those with normal glucose tolerance (P < 0.01, by chi(2) test). The prevalences of IGT and type 2 diabetes were significantly higher in FHxPOS PCOS women compared with FHxNEG PCOS women, IGT evident in 37 (35%) FHxPOS compared with 57 (19%) FHxNEG women, and type 2 diabetes evident in seven (7%) FHxPOS compared with nine (3%) FHxNEG women. Among the 392 nondiabetic subjects, after adjustment for the effects of race, FHxPOS differed significantly from FHxNEG patients in having a higher mean waist to hip ratio, hemoglobin A(1c) level, 2-h glucose level, fasting glucose and insulin levels, glucose to insulin ratio, homeostasis model assessment model of insulin resistance, and areas under the glucose and insulin curves during the oral glucose tolerance test. A family history of type 2 diabetes was present with a significantly greater frequency among women with PCOS who had IGT or type 2 diabetes compared with those with normal glucose tolerance. Conversely, a family history of type 2 diabetes in a first-degree relative was associated with a significantly higher risk for IGT or type 2 diabetes in women with PCOS. Even among nondiabetic women with PCOS, a positive family history of type 2 diabetes was strongly associated with metabolic characteristics associated with an increased risk for type 2 diabetes. Finally, the fasting glucose concentration was poorly associated with 2-h glucose concentrations among PCOS women with IGT, suggesting that the fasting glucose concentration is inadequate to predict the presence of IGT in PCOS.