BACKGROUND: Clinical implications of proximal optimisation technique (POT) for bifurcation lesions have not been investigated in a randomised controlled trial. AIMS: This study aimed to investigate whether proximal optimisation technique (POT) is superior in terms of stent apposition compared with the conventional kissing balloon technique (KBT) in real-life bifurcation lesions using optical coherence tomography (OCT). METHODS: A total of 120 patients from 15 centres were randomised into two groups: POT followed by side branch dilation or KBT. Finally, 57 and 58 patients in the POT and KBT groups, respectively, were analysed. OCT was performed at baseline, immediately after wire recrossing to the side branch, and at the final procedure. RESULTS: The primary endpoint was the rate of malapposed struts assessed by the final OCT. The rate of malapposed struts did not differ between the POT and KBT groups (in-stent proximal site: 10.4% vs. 7.7%, p=0.33; bifurcation core: 1.4% vs. 1.1%, p=0.67; core's distal edge: 6.2% vs. 5.3%, p=0.59). More additional treatments were required among the POT group (40.4% vs. 6.9%, p<0.01). At 1-year follow-up, only one patient in each group underwent target lesion revascularisation (2.0% vs. 1.9%). CONCLUSIONS: POT followed by side branch dilation did not show any advantages over conventional KBT in terms of stent apposition, however, the excellent mid-term clinical outcomes were observed in both strategies.