The KW39 stent is a balloon-expandable, stainless-steel, slotted-tube stent, newly designed to adjust to the shape of the coronary arteries. We evaluated the clinical efficacy and safety of KW39 stent-based percutaneous coronary interventions in human native coronary arteries. A total of 105 patients (110 lesions), with a diagnosis of stable angina, acute coronary syndrome, or asymptomatic myocardial ischemia, were included in this prospective study. The primary endpoint was the target-lesion revascularization rate at the conclusion of a 6-month follow-up period. The secondary endpoints were the rates of technical and procedural success and the rate of major adverse cardiac events (defined as cardiac death, myocardial infarction, and target-lesion revascularization) in the course of the 6 months after stent placement. The 6-month target-lesion revascularization rate was 8.6%. The KW39 stent was highly satisfactory in regard to all secondary endpoint comparisons. Binary (>50%) in-stent restenosis was observed in 22 of 110 lesions (20%). The mean diameter stenosis at 6 months after percutaneous coronary intervention was 35.1% ± 14.4%, and the mean late lumen loss was 1.06 ± 0.48 mm. Stepwise multivariate analysis showed probable causal associations between adverse local environments for stent implantation and the subsequent need for target-lesion revascularization. We conclude that KW39 stent implantation was technically feasible and clinically safe in the patient population that we studied. The results of the safety endpoints, including cardiac death and acute myocardial infarction, were acceptable.