The authors report a thirty-seven-year-old woman with systemic lupus erythematosus (SLE), a coronary aneurysm, and myocardial infarction. SLE was diagnosed at twenty-three years of age and treated with prednisolone. Seven years later, she developed inferior myocardial infarction, and coronary angiography showed an aneurysm in the proximal right coronary artery without associated stenosis. At the age of thirty-seven years, she died from cerebral infarction and sepsis. Autopsy revealed an aneurysm (6 mm in diameter) in the proximal right coronary artery and an old inferior myocardial infarction. Histologic examination showed recanalization and fibrosis in the media of the aneurysm wall. This case suggests that coronary aneurysm may cause myocardial infarction in SLE and that aneurysm formation may be a sequela of arteritis.