BACKGROUD: The provisional approach is now regarded as the standard technique for most bifurcation lesions. However, the optimal indication for side branch (SB) ballooning and/or stenting is unknown. METHODS: The present trial was a prospective, randomized, open-label, single-center trial comparing the 2 strategies (conservative vs. aggressive) for SB intervention during coronary bifurcation stenting. A total of 258 patients with bifurcation lesion (SB diameter 2.3mm) treated with drug-eluting stent (DES) were randomized either to conservative or aggressive strategy for SB ballooning and/or stenting. In the conservative group, SB ballooning was done if Thrombolysis In Myocardial Infarction (TIMI) flow <3 on the SB in non-left main bifurcation (LM) subgroup, and diameter stenosis (DS) >75% in left main bifurcation (LM) subgroup, after MV stenting. SB stenting was performed if TIMI flow <3 in the SB after ballooning in non-LM subgroup, and DS >50% or dissection in the SB after ballooning in LM subgroup. In the aggressive group, SB ballooning was done if DS >75% on the SB in non-LM subgroup, and DS >50% in LM subgroup, after MV stenting. After SB ballooning, SB stenting was performed if DS >50% on the SB in non-LM subgroup, and DS >30% or dissection on the SB in LM subgroup. If SB stenting was indicated, the T-stenting and small protrusion technique was used. The primary end point was target vessel failure (TVF): cardiac death, myocardial infarction (MI), or target vessel revascularization for 9 months. RESULTS: Baseline clinical and angiographic characteristics were similar between 2 groups. Left main bifurcation lesion was noted in 114 patients (44%) and true bifurcation lesion in 171 patients (66%). Nine-month clinical follow-up was available in all patients, and 9-month angiographic follow-up in 84%. SB dilation after MV stenting was more frequently required in the aggressive group than in the conservative group (70.0% vs. 25.0%, p<0.001). SB stenting after SB dilation was more frequently required in the aggressive group than in the conservative group (30.0% vs. 7.8%, p <0.001). The aggressive group was associated with a significantly higher incidence of peri-procedural MI compared to the conservative group (16.2% vs. 7.8%, p=0.04). At 9 months, the incidence of TVF was similar in the 2 groups (7.7% in aggressive group vs. 8.6% in conservative group, p=0.79). The result of 9-month angiographic follow-up will be presented. CONCLUSION: The conservative strategy for SB ballooning and/or stenting was not associated with increased incidence of clinical events compared to the aggressive strategy in patients undergoing coronary bifurcation stenting with DES.