BackgroundColorectal liver metastases attached major intrahepatic vessels has been considered to be a risk factor for survival outcome after liver resection. The present study aimed to clarify the outcomes of R1 surgery (margin < 1 mm) in CRLM patients, distinguishing parenchymal margin R1 and attached to major intrahepatic vessels R1.MethodsIn present study, 283 CRLM patients who were evaluated to be attached to major intrahepatic vessels initially and underwent liver resection following preoperative chemotherapy. They were assigned to two following groups: R0 (n= 167), R1 parenchymal (n= 58) and R1 vascular (n= 58). The survival outcomes and local recurrence rates were analyzed in each group.ResultsOverall, 3- and 5-year overall survival rates after liver resection were 53.0% and 38.2% (median overall survival 37 months). Five-year overall survival was higher in patients with R0 than parenchymal R1 (44.9%% vs. 26.3%,p= 0.009), whereas there was no significant difference from patients with vascular R1 (34.3%,p= 0.752). In the multivariable analysis, preoperative chemotherapy > 4 cycles, clinical risk score 3–5, RAS mutation, parenchymal R1 and CA199 > 100 IU/ml were identified as independent predictive factors of overall survival (p< 0.05). There was no significant difference for local recurrence among three groups.ConclusionParenchymal R1 resection was independent risk factor for CRLM. Vascular R1 surgery achieved survival outcomes equivalent to R0 resection. Non-anatomic liver resection for CRLM attached to intrahepatic vessels might be pursued to increase patient resectability by preoperative chemotherapy.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12893-023-01971-2.