The degrees of cross-sectional area luminal narrowing by atherosclerotic plaques of each 5 mm long segment of each of the four major (right, left main, left anterior descending and left circumflex) epicardial coronary arteries in 22 necropsy patients (age 16 to 37 years, 21 women) with systemic lupus erythematosus (SLE) was determined, and the findings were compared to those in 13 control subjects. Of 623 coronary segments (5 mm long) in the patients with SLE, 80 (13 percent) were narrowed 76 to 100 percent (controls = 0 of 431 segments); 125 (20 percent), 51 to 75 percent (controls = 6 percent); 273 (44 percent), 26 to 50 percent (controls = 31 percent). Of the 22 patients with SLE, 10 had one or more of the four major coronary arteries narrowed 76 to 100 percent in cross-sectional area, and 12 patients had lesser degrees of narrowing similar to that in the 13 control subjects. The 10 patients with SLE and severe coronary narrowing compared to the 12 patients with SLE and no severe (greater than 75 percent) coronary narrowing had significantly higher (1) mean values of total serum cholesterol (382 versus 290 mg/dl), (2) mean systolic/diastolic systemic arterial pressures (175/119 versus 151/93 mm Hg), (3) frequencies of mitral valvular disease (seven of 10 patients versus none of 12 patients) and (4) frequencies of pericardial adhesions (seven of 10 patients versus three of 12 patients).