Introduction: A classification system is needed to stratify patients undergoing open liver resection (OLR). The present report aimed to evaluate OLR procedures based on a previously-described laparoscopic liver resection classification (Ann Surg.2018), using operative time, blood loss, and comprehensive complication index (CCI). Method: Consecutive 3707 patients who underwent OLR were included. Patients who underwent multiple wedge/segmentectomy, vascular/biliary reconstruction, and concomitant extra-hepatic procedures were excluded. Wedge/segmentectomy was divided into anterolateral (Couinaud's segments 2, 3, 4b, 5, and 6) and posterosuperior (segments 1, 4a, 7, and 8) segments. Eleven OLRs were divided into 3 groups according to scores based on less (score 0) or more (score 1) than median/mean values of operative time, blood loss, and CCI. Results: Of 3,707 OLRs, 2,047 were selected. Median operative time, median blood loss, and mean CCI were 145 min, 200 ml, and 10.4, respectively. Group I (0 point) included wedge resection and left lateral sectionectomy. Group II (1 points) included anterolateral segmentectomy and left hepatectomy. Group III (2-3 points) included posterosuperior segmentectomy, right hepatectomy, right posterior sectionectomy, central hepatectomy, and extended left/right hepatectomy (Table 1). The 90-day mortality rates (Groups I, II, and III: 0.5%, 1.3% and 2.9%) and major complication rates (4.1%, 8.3%, and 15.2%) were associated with increase from Groups I to III (all P< 0.001, trend test). Conclusions: This classification provides three-level stepwise OLR difficulty: Group I (low), Group II (intermediate), and Group III (high). This can be useful for surgical education and to benchmark surgical procedures.Tabled 1EP01C-090 Table 1Perioperative outcomes by ProceduresWedge-AL†Wedge-PS‡Left lateralSeg-AL†Left HepSeg-PS‡Right HepEx- Right HepRight posteriorColini HepIi-LeA HepTttitNumber1967212125320610860731625171262047OR time, minMedian117133110152120198140196250320246145IQR78-145108-19480-14399-201184-200146-270108-235120-295233-315251-375148-330105-236Blood loss, mLMedian100110125100200200300300225250300200IQR50-20056-25088-20075-250100-313100-300200-500200-600150-525150-500200-470100-400MorbidityCCI§Mean5.25.75.47.47.58.012.816.69.210.311.710.4SD12.411.313.115.314.516.120.521.87.110.911.618.1A1I complication18.925.020.726.526.330.643.256.028.035.340.936.0Major complication4.14.24.15.911.29.213.219.016.023.518.3911.590-day mortality0.500.81.21.503.14.14.001.62.1Score¶00011223223GroupIIIIIIAbbreviations; Wedge-AL, wedge resection of anterolateral segment; Wedge-PS, wedge resection of posterosuperior segment; Left lateral, left lateral sectionectomy; Seg-AL, anterolateral segmentectomy; Left Hep, left hepatectomy; Seg-PS, posterosuperior segmentectomy; Right Hep, right hepatectomy; Ex-Right Hep, extende right hepatectomy; Right posterior, right posterior sectionectomy; Central Hep, central hepatectomy; Ex-Left Hep, ectended left hepatectomy; IQR, interquartile range; CCI, comprehensive complication index;SD, standard deviation.†Couinaud’s segments 2, 3, 4b, 5, and 6; ‡Couinaud’s segments 1, 4a, 7, and 8§Defined by Slankamenac et al.¶One point was allocated as follows; either operative time (145 min and more), the amount of blood loss (200 mL and more), or CCI (10.4 and more). Open table in a new tab Abbreviations; Wedge-AL, wedge resection of anterolateral segment; Wedge-PS, wedge resection of posterosuperior segment; Left lateral, left lateral sectionectomy; Seg-AL, anterolateral segmentectomy; Left Hep, left hepatectomy; Seg-PS, posterosuperior segmentectomy; Right Hep, right hepatectomy; Ex-Right Hep, extende right hepatectomy; Right posterior, right posterior sectionectomy; Central Hep, central hepatectomy; Ex-Left Hep, ectended left hepatectomy; IQR, interquartile range; CCI, comprehensive complication index; SD, standard deviation. †Couinaud’s segments 2, 3, 4b, 5, and 6; ‡Couinaud’s segments 1, 4a, 7, and 8 §Defined by Slankamenac et al. ¶One point was allocated as follows; either operative time (145 min and more), the amount of blood loss (200 mL and more), or CCI (10.4 and more).