Context and Objective: Total muscle triglyceride (MT) content has been associated with insulin resistance. We investigated the predictors and impact of MT on relevant metabolic parameters including peripheral and hepatic insulin resistance in elderly twins. Design and Participants: Seventy-four elderly same-sex twins underwent hyperinsulinemic euglycemic clamps preceded by an iv glucose tolerance test. Aerobic capacity (VO(2max)) and body composition (dual-energy x-ray absorptiometry scan) were determined in all twins. A biopsy from the vastus lateralis muscle was excised in the fasting state. The muscle triacylglycerol content was analyzed by biochemical extraction from these biopsies. Results: The percentage of total body fat was the only independent predictor of MT content. After adjustment for trunk fat percentages and sex, MT level was significantly associated to fasting plasma levels of glucose and insulin as well as hepatic insulin resistance. However, the association was weakened after adjustment for total fat percentages. A 1 sd (34.5 mmol/kg dry weight) increase in MT content was associated with a 24% increase of hepatic insulin resistance. No association between MT content and peripheral insulin sensitivity was observed. Conclusion: MT content is associated with hepatic but not peripheral insulin resistance in elderly twins. We speculate that MT content may reflect the general ectopic accumulation of triglycerides, including fat in the liver.