The insulin resistance syndrome (IRS) is characterized by a constellation of interrelated coronary heart disease (CHD) risk factors, including dyslipidemia, obesity, central obesity, elevated systolic blood pressure, and hyperinsulinemia. Factor analysis was used to investigate the clustering of these risk factors in individuals by examining the correlational structure among these variables. Data from 281 genetically unrelated nondiabetic women who participated in exam 2 (1979 to 1980) of the Kaiser Permanente Women Twins Study were used. Factor analysis reduced 10 correlated risk factors to 3 uncorrelated factors, each reflecting a different aspect of the IRS: factor 1 (increased body weight, waist circumference, fasting insulin, and glucose), factor 2 (increased postload and fasting glucose and insulin and systolic blood pressure), and factor 3 (larger low-density lipoprotein particles, decreased plasma triglycerides, and increased high-density lipoprotein). Together, the factors explained nearly 66% of the total variance in the data. Thus, factor analysis defined three distinct aspects of the IRS in this sample of nondiabetic women. These factors may reflect separate underlying mechanisms of the syndrome, each of which may also be involved in CHD risk.