Directional coronary atherectomy, a new transluminal procedure for treatment of obstructive lesions in coronary arteries by excision and removal of tissue, was performed on 447 lesions in 382 procedures. Successful outcome, defined as a reduction of stenosis by greater than or equal to 20% with a less than 50% residual stenosis, was achieved in 89.5% of lesions and mean stenosis was reduced from 75.9 +/- 13.3% to 14.5 +/- 22.1% (p less than 0.001). Complications included vessel occlusion during the procedure, 2.4%; vessel occlusion after the procedure, 1.3%; new lesion, 0.5%; nonobstructive guiding catheter-induced dissection, 0.3%; perforation, 0.8%; distal embolization, 2.1%; Q wave myocardial infarction, 0.8% and non-Q wave myocardial infarction, 4.2%. Twelve patients (3.1%) required coronary artery bypass surgery for these complications. The atherectomy success rate was greater than 80% and the combined atherectomy and angioplasty success rate was greater than 90% for complex morphologic features such as eccentric lesions, lengthy lesions, lesions with abnormal contour, angulated lesions, ostial lesions and lesions with branch involvement. In the presence of calcific deposition, atherectomy success rate was 52% for primary lesions and 83% for restenosed lesions. Among angiographically complex lesions, calcium was the predictor for failed atherectomy (p less than 0.0001). In summary, directional coronary atherectomy is safe and effective for treatment of obstructive lesions in coronary arteries in selected cases. In particular, it achieves a high success rate in lesions with complex morphologic characteristics, such as eccentricity, abnormal contour and ostial involvement.