Objectives The aim of this study was to describe the procedural aspects and outcomes of retrograde chronic total occlusion (CTO) percutaneous coronary intervention (PCI) through ipsilateral collateral channels (ILCs). Background Retrograde CTO PCI via ILCs is rarely performed, usually when no other retrograde options exist, and available evidence derives mostly from case reports. Methods A large retrospective multinational registry was compiled, including all consecutive patients undergoing retrograde CTO PCI through ILCs at 6 centers between September 2011 and October 2016. Success rates, as well as procedural complications and in-hospital outcomes, were studied. Results A total of 126 patients (17% of all retrograde CTO PCIs) were included. The mean age was 65.7 ± 11.2 years, and the mean J-CTO (Multicenter CTO Registry in Japan) score was 2.36 ± 1.13. The target vessel was the circumflex coronary artery in 42%, the left anterior descending coronary artery in 39%, and the right coronary artery in 19%. The ILCs used were epicardial in 76% and septal in 24%. ILC anatomy was very heterogeneous. One guiding catheter was used in 80%, whereas the ping-pong technique was used in 20%. A retrograde wire could be advanced to the distal cap in 81%. Technical and procedural success rates were 87% and 82%, respectively. ILC perforation with need for intervention was observed in 5.6% and tamponade due to ILC perforation in 2.4%. One patient (0.8%) died. Conclusions Retrograde CTO PCI through ILCs is a challenging intervention that can be performed in difficult occlusions with high success rates and reasonable rates of complications by experienced operators.