Abstract Background Considerable progress in the treatment of coronary bifurcation lesions has been achieved. Side branch pre-dilatation (SPPD) is a technique that is generally not recommended by the latest guidelines and consensus statements. The main reason is the risk of side branch (SB) dissection or vessel closure. Aim The aim of the current study is to explore the rates of SB closure in patients undergoing bifurcation PCI with or without SB pre-dilatation. Methods All patients with coronary bifurcation lesions treated between 2012 and 2022 were included in the prospective registry. For the current analysis, only patients with stable or unstable angina were included, with follow-up of at least two years. Patients with STEMI and left main stenosis were excluded. Propensity Score Matching (PSM) was performed to equalize the effects of the following characteristics: age, sex, diabetes, smoking, hypertension, dyslipidemia, renal failure, cancer, COPD, atrial fibrillation, left ventricular ejection fraction, and SYNTAX score. SB closure was defined as SB ostial stenosis ≥99% with TIMI 0-1 flow. Results 832 patients from the registry covered the criteria for the current analysis. After PSM, 324 matched couples remained, and 648 patients were analyzed. The demographic characteristics of SBP(+) and SBP (-) were well balanced, with no differences between groups – age 68±10 years, 71% males, 40% smokers, 47% with diabetes, 26% with previous MI, 53% with previous PCI, 4% after CABG, 12% with peripheral arterial disease, 13% with COPD, 32% with renal failure, 23% AFib, LVEF 55±10%. Patient with SBP(+) wad more CTOs (17% vs. 9%, p=0.003), longer lesions (42±21mm vs. 36±20mm, p<0.001) and more severe SB stenoses (68%±25% vs. 41%±31%, p<0.001). Among true bifurcation stenoses (Medina xx1 – 63%, 410/648), 88% were predilated. SB closure was non-significantly different in groups with SBPD and SBnPD (3.6% vs. 2.2%, p=0.272). Acute SB closure after stenting occurred at similar rates in SBPD and SBnPD groups (3.6% vs. 2.7%, p=0.505), without difference in rates of MI if SB was closed or not (n=10/17, 59% vs. n=227/631, 36%, p=0.058). The rate of periprocedural MI was not significantly different between groups with and without SB closure – 52% vs. 34%, p=0.066. At the end of the procedure, only 7 SBs were closed, 2 in the SBPD group and 5 in the SBnPD group (p=0.461). Conclusions The rates of final SB closure were numerically lower (but not significantly different) when SBPD was performed. SB closure did not translate into worse clinical outcomes.