This study examined the accuracy of a triglyceride/high-density lipoprotein (HDL) cholesterol ratio of 3.8 for the prediction of low-density lipoprotein (LDL) phenotype B. The ratio of 3.8 was based on Adult Treatment Panel recommendations for normal fasting triglycerides (<150 mg/dl) and HDL cholesterol (>40 mg/dl). Fasting blood samples were obtained from 658 patients. LDL phenotype analysis was performed by nuclear magnetic resonance spectroscopy. A triglyceride/HDL cholesterol ratio of 3.8 divided the distribution of LDL phenotypes with 79% (95% confidence interval [CI] 74 to 83) of phenotype B greater than and 81% (95% CI 77 to 85) of phenotype A less than the ratio of 3.8. The ratio was reliable for identifying LDL phenotype B in men and women.