Approximately 30% of patients with colorectal cancer and liver metastases present with synchronous disease.(Manfredi) Resection of colorectal cancer metastases confined to the liver has been shown to offer long-term survival.(Norlinger; Robertson; Nordlinger) However, the optimal timing of surgical resection of synchronous liver metastases in relation to the primary tumour is not well defined. Prior retrospective cohorts and meta-analyses suggest that the simultaneous approach carries similar postoperative complication and perioperative mortality rates.(Slesser; Yin; Martin; Chua; Feng; Reddy; Jarnagin; Capussotti) Most of these reports however, carry a significant selection bias, as surgeons tend to combine limited liver resections and "straightforward" colorectal resections as opposed to complex resections. Recent studies suggest that the postoperative complication risk is similar even in the case of complex liver resections as well as complex colon resections and rectal cancer resections.(Silberhumer; Vigano) Rectal resections when compared to colon resections are thought to be more complex, due to: a higher risk of anastomotic leakage,(Rullier) the use of specific surgical procedures, such as total mesorectal excision (Heald, MacFarlane) and laparoscopic surgery(Bonjer) and the involvement of a multidisciplinary team to determine the use and timing of neoadjuvant chemoradiotherapy.(Jeong; Kapiteijn) The conclusion of these studies was that further data from prospective randomized studies is needed in order to determine whether simultaneous resection is efficient and safe. Improvements in anesthesia, critical care and surgical resection techniques for both liver and colorectal surgery have enabled innovative surgeons and institutions to perform simultaneous resections in complex liver and colorectal cases in a safe manner, and the simultaneous approach has been adopted by many surgeons despite the lack of studies with rigorous methodology to provide good quality data.