Although a strong genetic susceptibility has been established for NIDDM and a maternal transmission of the disease predominates in some populations, a relationship between parental diabetes status and metabolic abnormalities in nondiabetic offspring has not been shown in humans. To address this question, we studied 2,152 first-degree relatives of patients with NIDDM (FH+) and 528 age- and weight-matched spouses without a family history of NIDDM (FH-) in Western Finland (the Botnia study). A subset of the subjects underwent a euglycemic insulin clamp combined with indirect calorimetry to measure insulin sensitivity and energy expenditure. Despite similar amounts of total body fat, persons with a family history of NIDDM had a greater waist-to-hip ratio (WHR) than spouses without a family history of diabetes (P < 0.003). They also had a decreased resting metabolic rate (P = 0.005), but this difference disappeared when adjusted for the difference in WHR. Insulin-stimulated glucose metabolism (P = 0.002), particularly nonoxidative glucose metabolism (P = 0.009), was reduced in FH+ compared with FH- subjects, and this difference remained after adjustment for WHR. A parental history of NIDDM influenced the insulin response to the oral glucose load, with male offspring of diabetic mothers showing the lowest insulin values (P = 0.011). Moreover, a parental effect was also observed on HDL and HDL2 cholesterol concentrations with female offspring of diabetic mothers showing lower values than female offspring of diabetic fathers (both P < 0.002). We conclude that abdominal obesity, insulin resistance, and decreased resting metabolic rate are characteristic features of first-degree relatives of patients with NIDDM and that the decrease in resting metabolic rate is partially related to the degree of abdominal obesity. A sex-specific paternal effect was observed on insulin and HDL cholesterol concentrations. Therefore, one has to consider the possibility of unprecedented maternal or paternal inheritance of different NIDDM phenotypes.