From January 1970 to December 1986, 2.7% (228/8509) of all patientshaving coronary artery bypass grafting had atherosclerotic coronary ostialstenosis of 50% or more. There were 126 males (55%) and 102 females (45%)with mean ages of 60.2 +/- 9.0 and 59.2 +/- 10.2 years (P = NS),respectively. The left ostium was involved in 176 (77.2%) patients, theright in 41 (18.0%) and both in 11 (4.8%). Isolated ostial stenosis (noassociated coronary disease of 50% or more) was present in 38/228 (17%)with females predominating (29/38, 76%). Isolated ostial stenosis occurredmore frequently on the right (10/41, 25%) than on the left (18/176, 16%).Associated coronary disease occurred in a single vessel in 42 patients, intwo vessels in 72 and in three vessels in 76 resulting in a mean of 2.0diseased vessels per patient. If patients with isolated ostial stenosis areexcluded there were 2.3 diseased arteries per patient. There were 687grafts performed in these patients, an average of 2.3 grafts per patient.One month surgical mortality was 4.8% (11/228), but has been 2% (2/104) inthe last 4 years. Nine of 27 late deaths were noncardiac with a meanfollow- up of 49 +/- 44 months. Ostial stenosis is hemodynamicallyequivalent to left main disease when the left ostium is involved.Symptomatic ostial lesions, whether right or left, require operativetherapy.