Among 6,200 patients undergoing coronary arteriography using the Sones technique at the Juntendo University Hospital and the Juntendo Urayasu Hospital from 1975 to 1988, 121 patients (1.95%, 111 males and 10 females) were found to have significant (> or = 50%) stenosis in their left main trunks (LMT). Patients with systemic inflammatory disease such as syphilis or Takayasu's arteriitis, aortic valvular disease, or a history of mediastinal irradiation were excluded from this study. Stenotic lesions of the LMT were categorized into 7 types according to their locations and appearances. 1. The most common type was stenosis localized just before the branching from the left circumflex artery (42 patients or 34.7%). 2. Although the incidence of left coronary ostial stenosis was not very high (13 patients, 10.7%) as a whole, that for the female patients was the highest (30.8%) of the 7 types. Nine patients showed atherosclerotic irregularities with or without significant stenosis in the distal coronary arterial trees. Four patients, including 3 women, were diagnosed as "primary solitary ostial stenosis" of which the cause is unknown. All of the 3 women were premenopausal, and their clinical profiles were as follows: Case 1 (45-year-old): She was hospitalized because of anterior chest pain during exertion or at rest. Her electrocardiogram (ECG) showed severe ischemic ST-T changes. Coronary cineangiography disclosed a 95% stenosis in the left coronary ostium, and the distal portion of the coronary artery was normal. She had not experienced angina after her coronary artery bypass operation. Case 2 (45-year-old): She was hospitalized because of exertional chest pain.(ABSTRACT TRUNCATED AT 250 WORDS)