We evaluated 37 patients (39 lesions, 11 women/26 men, median age of 66 years old) with coronary ostial lesions who underwent cutting balloon angioplasty (CB). Seventy-four patients (78 lesions, 18 women/56 men, median age of 65 years old) who had undergone plain old balloon angioplasty (POBA) for coronary ostial lesions were also enrolled as the control group. At clinical diagnosis, unstable angina was seen in 8.1% of the CB group and in 9.5% of the POBA group. Post myocardial infarction silent ischemia was seen in 28.3% of the POBA group and 32.4% of the CB group. The success rate was 94.8% in the CB group and 84.6% in the POBA group. The frequency of intimal dissection was not significantly different between the two groups. However, all cases of intimal dissection in the CB group were mild (either type A or B), whereas the POBA group included many cases of severe intimal dissection (types B through F). No cardiac event was observed in the CB group. However, in the POBA group, cardiac death occurred in 1.4% and emergency bypass surgery occurred in 0.7% of the patients. Calculating the restenosis rate based on the cumulative percent diameter stenosis curve resulted in 43% for the CB group and 53% of the POBA group. We concluded that the cutting balloon was useful for ostial lesions as compared to plain old balloon angioplasty.