Low levels of high-density lipoprotein (HDL) cholesterol are a marker of coronary artery disease progression and are associated with cardiovascular events. However, whether low HDL cholesterol is a useful prognostic indicator after percutaneous coronary intervention (PCI) is not known. In a sample of 4,088 patients who underwent PCI we evaluated 1-year mortality and repeat revascularization as a function of baseline HDL levels classified into approximate quartiles of very low (<35 mg/dl), low (35 to 40 mg/dl), medium (41 to 47 mg/dl) and high (48 to 120 mg/dl) HDL cholesterol. Decreasing levels of HDL cholesterol were associated with younger age, male gender, smoking, diabetes mellitus, and a history of bypass surgery (p <0.0001 for all). One-year mortality and coronary revascularization were significantly higher in the very low HDL cholesterol group compared with the other groups (very low HDL cholesterol 6.5% and 25.4%, respectively; low HDL cholesterol 3.1% and 20.8%; medium HDL cholesterol 4.3% and 22.7%; high HDL cholesterol 3.1% and 20.6%, p = 0.0001 and p = 0.007). One-year mortality was significantly higher in men with an HDL cholesterol level <33 mg/dL and in women with an HDL cholesterol level <38 mg/dL. In multivariable analysis, very low HDL was associated with nearly twofold the risk of death after adjusting for other independent predictors of outcome. In conclusion, in patients with coronary artery disease undergoing PCI, a baseline HDL cholesterol level <35 mg/dl is an important prognostic indicator. Baseline HDL cholesterol levels <33 mg/dl for men and <38 mg/dl were associated with higher one-year mortality after PCI.