Background: Despite published guidelines and availability of many effective lipid-altering therapies, dyslipidemia in the United States remains largely underdiagnosed and undertreated. Methods: This study used data from the 1999-2000 National Health and Nutrition Examination Survey to assess the current state of dyslipidemia management in the US adult population compared with guidelines issued by the Third Adult Treatment Panel of the National Cholesterol Education Program. Percentages were weighted to reflect population estimates, computed using SUDAAN (Research Triangle Institution, Cary, NC). Results: Among 1425 respondents aged ≥20 years with complete data, 29.5% were eligible for therapeutic lifestyle changes (TLCs, 16.0%) or lipid-lowering drug therapy (LDT, 13.4%). Among high-risk adults, 79.3% were eligible for either TLC (35.7%) or LDT (43.6%). Only 43.7% of treatment-eligible adults reported ever being diagnosed with dyslipidemia. Of those diagnosed, 77.4% reported being told to undertake TLC, and 34.2% reported being told to take LDT. Of adults eligible for drug therapy, the average percentage reduction in low-density lipoprotein cholesterol (LDL-C) required to reach goal was 28.0% (standard error [SE] 1.1), and 41.9% required a reduction of >30% in LDL-C to reach goal. Of high-risk adults eligible for drug therapy, the average required reduction was 36.9% (SE 1.4), and 76.3% required a reduction of >30% in LDL-C. Conclusions: Despite advances in dyslipidemia therapy and changes in guidelines over the last decade, LDL-C continues to be inadequately managed among US adults. Of particular concern is the undertreatment of high-risk patients and failure of many treated patients to achieve LDL-C goal.