The Micro stent (MS) is a balloon expandable stent that allows the treatment of stenoses in distal and tortuous coronary arteries. This prospective study was performed to evaluate initial and late results of MS implantations. A total of 127 MS (101 in native coronary arteries and 26 in saphenous vein grafts) were implanted in 85 patients (1.5 stents/pt, 65 male, and 20 female, age 62, +/-10 yr) with angina pectoris class II-III: 21 (25%), angina pectoris class IV: 41(48%), and acute myocardial infarction: 23 (27%). Indications per segment treated (n=93): elective: 49 (53%); suboptimal balloon angioplasty (PTCA) result: 33 (35%); bailout: 11 (12%). The patients were discharged with 100 mg of aspirin daily unless other indications for oral anticoagulants were present. Procedural success (diameter stenosis of 30% without the occurrence of clinical events within 3 wk) was 85%. Early clinical events (<3 wk included: death:1%; subacute closure: 5%; coronary artery bypass surgery (CABG): 1%; vascular complications: 4%. Late clinical events (3 wk-6 mo) included: acute myocardial infarction:3%, PTCA 5%, CABG 3%, angina class Ill-IV: 4%. Quantitative angiographic results were: the minimum lumen diameter increased from 0.90+/-0.72 before to 3.05+/-0.48 mm (<P0.001) after stent implantation. At follow-up, which was 5.5 mo +/-1.1 mo, 61/79 pts (77%), the loss in diameter was 0.90+/-0.68 mm. The net gain was 1.26+/-0.90 mm. The restenosis rate (diameter stenosis > 50% at FU) was 13%. This study demonstrates high procedural and late success rates of Micro stent implantations.