Percutaneous coronary intervention (PCI) for true bifurcation lesions is challenging. Although the jailed balloon protection technique is an established method with which to prevent side branch occlusion during the treatment of bifurcation lesions, little is known regarding the potential risks of this technique. We describe a 71-year-old man with exertional angina pectoris who was treated with PCI for a calcified true bifurcation lesion in the left anterior descending artery and diagonal branch. After performing rotational atherectomy (1.75 mm burr) for the main vessel and pre-dilatation for both the main vessel and side branch, we performed the jailed balloon technique to protect the large diagonal branch during stent implantation. However, the jailed balloon was entrapped after main vessel stent balloon inflation. The entrapped jailed balloon was then inflated again and successfully removed after balloon deflation, but significant stent deformation was seen with intravascular ultrasound imaging. Fortunately, post-dilatation was successfully performed with a non-compliant balloon, and a final coronary angiogram showed acceptable results. This case report and literature review highlights a potential risk of the jailed balloon technique and conceivable alternatives during PCI for true bifurcation lesions.