Background: The fasting serum lipid profile [triglycer-

ides (TGs), total cholesterol (TC), and LDL- and HDL-cholesterol (LDL-C and HDL-C)] is used to calculate lipid ratios (TC/HDL-C, LDL-C/HDL-C, TG/HDL-C) that allow identification of individuals at increased risk for cardiovascular disease. Because these individuals are also frequently insulin resistant, this study analyzed the relationships between lipid ratios and insulin sensitiv-ity. Methods: In 132 obese [mean (SE) body mass index, 37.5 (0.6) kg/m2] outpatients without known diabetes mellitus, fasting serum lipid profiles and 75-g oral glucose tolerance tests were performed. Insulin sensitiv-ity was assessed from surrogate estimates for fasting (QUICKI) and dynamic (OGIS) conditions. Results: After exclusion of other endocrine diseases (n 35), the remaining patients were classified as glucose tolerant (n 56), glucose intolerant (n 22), or as having type 2 diabetes (n 19). QUICKI and OGIS indicated severe insulin resistance in all individuals with type 2 diabetes and impaired glucose tolerance compared with glucose-tolerant individuals: QUICKI, glucose tolerant, 0.302 (0.002); glucose intolerant, 0.290 (0.002); type 2 diabetes, 0.281 (0.005); P <0.001; OGIS (mL m2 min1), glucose tolerant, 343 (7), glu