- Introduction: The "traditional approach" to resect synchronous colorectal cancer with liver metastases (CRLM) is to perform staged resections. Many institutions perform simultaneous resection. Disadvantages to the simultaneous approach include longer operating room times, which may increase major postoperative complication rates. Data supporting simultaneous resection are limited to retrospective studies that are subject to selection bias. Therefore, we have proposed a single-arm prospective cohort pilot study to evaluate the postoperative complications following simultaneous resection of synchronous CRLM. Methods and analysis: This single-arm study will be performed in five high-volume hepatobiliary centres to prospectively evaluate the following objectives: (1) To determine the 90-day postoperative complication rate of patients diagnosed with synchronous CRLM undergoing a simultaneous colorectal and liver resection, including major liver resections; (2) To determine the postoperative mortality rate at 90 days following index surgery; (3) To determine change in global health-related Quality of Life (QoL) following simultaneous resection at three months compared to baseline; and (4) To build a costing model for simultaneous resection, We will also evaluate the feasibility of performing combined resection in these patients by evaluating the number of eligible patients enrolled in the study and determining the reasons eligible patients were not enrolled. This protocol has been registered with ClinicalTrials.gov (NCT02954913). Ethics and dissemination: This study has been provincially approved by the central research ethics board. Study results will inform the design a randomized controlled trial by providing information about the comprehensive complication index in this patient population used to calculate the sample size for the trial.