The relation of alcohol consumption to serum lipids and the severity of coronary atherosclerosis was examined in 212 men undergoing coronary angiography. The severity of coronary atherosclerosis was assessed in terms of the presence of greater than or equal to 75% diameter stenosis and the Gensini severity score. Alcohol consumption was divided into 4 categories: none (0 ml alcohol/week), light (1 to 100 ml alcohol/week), moderate (101 to 300 ml alcohol/week) and heavy (greater than or equal to 301 ml alcohol/week). Alcohol consumption was positively related to high-density lipoprotein cholesterol and inversely related to total cholesterol, but was not associated with triglyceride. After adjustment for these serum lipids as well as for cigarette smoking and systemic hypertension, the risk of coronary stenosis was significantly decreased in the moderate drinkers. A decreased risk among moderate drinkers also was noted in terms of Gensini's severity score. These findings suggest that moderate alcohol consumption may protect against severe coronary atherosclerosis.