BACKGROUND: The aim of this study was to retrospectively validate a new system to predict perihilar cholangiocarcinoma (PHC) resectability. We hypothesized that when the left lateral section (segments II-III) duct confluence (LLC) is free, the left lateral section might be preserved for curative resection. When the LLC is invaded, vascular invasion is frequent and radical resection might often be impossible without complex vascular reconstruction. METHOD: Radiological files of patients operated for PHC at our institution were reviewed and PHC was classified depending on whether LLC was invaded (type X) or free (type Y). Peroperative findings and follow-up were then matched with our XY classification. RESULTS: Thirty-seven patients were included, 28 (78 %) type Y and nine (22 %) type X PHCs. Hepatic artery (HA) invasion was present in 14 % of type Y and 100 % of type X PHCs (P < 0.001). Left HA was never involved in type Y and always involved in type X. Portal vein invasion was present in 25 and 78 % of type Y and type X PHC, respectively (P = 0.014). Complete resection rates without HA in type Y and X patients were 89 % (84 % R0 and 16 % R1) and 33 % (37.5 % R0 and 12.5 % R1), respectively (P = 0.01). Sensitivity, specificity, and precision of the XY classification to predict resectability were 84, 67, and 84 %, respectively. CONCLUSION: XY classification for PHCs suggests that in type Y (free LLC), the tumor is most often resectable, while in type X (LLC involved), the tumor is only resectable using complex vascular reconstructions.