Abstract(#br) Background(#br)In terms of timing of resection for synchronous liver metastases from colon cancer, some reports recommend leaving an interval (e.g., 3 months) after primary colorectal resection, because of reports of occasional and rapid remnant recurrence of residual liver metastases after simultaneous colorectal and liver resection (LR). For patients with metachronous liver metastasis (MLM), we prospectively examined the appropriateness of a 3-month interval to LR (i.e., delayed resection) following initial detection of hepatic lesions from the viewpoints of (1) detection of new metastases during this interval and (2) postoperative outcome.(#br) Methods(#br)Seventy-nine consecutive patients with modified Japanese criteria H1 class MLM (i.e., ≤4 nodules, 6 cm or less in... diameter) and without obvious extrahepatic lesions, presenting between 1990 and 2008, were included in this study. Between 1990 and 2001, 52 patients were treated by LR without an interval (i.e., nondelayed group); from 2002, 27 patients were prospectively scheduled for LR at an interval of 3 months after initial detection of metastases (i.e., delayed group). During the 3-month interval, no adjuvant chemotherapy was given. Just prior to LR, patients were re-evaluated using computed tomography (CT) and deoxy-2-[18F]fluoro- d -glucose positron emission tomography (FDG-PET) to exclude cases unsuitable for surgery.(#br) Results(#br)Out of 27 patients in the delayed group, 2 (7.4%) did not undergo LR after the 3-month interval and were excluded from the analysis: one because of multiple nodules in the bilateral lobe of the liver with pulmonary metastases and another because of para-aortic lymph node metastasis. Of the 25 patients for whom LR was indicated, 24 underwent LR as initially planned. In the remaining patient, after the 3-month interval, invasion of the tumor had occurred into the inferior vena cava (IVC) and other surgery in addition to the planned operation was required. When comparing the postoperative outcome data of the delayed group ( n = 25) with the nondelayed group ( n = 52), overall early recurrence within 1 year after LR was noticed in 30.9% (16/52) of the nondelayed group and 28.0% (7/25) of the delayed group; the incidence of only early extrahepatic recurrence decreased 5.1% in the delayed group (21.1% versus 16.0%, respectively). When comparing disease-free survival after liver resection, however, there was no significant difference between the groups.(#br) Conclusions(#br)Delayed LR for MLM patients after initial detection of hepatic lesions is of no clinical benefit. Only in cases when extrahepatic lesions with MLM are suspected could an interval make such lesions clearer and assist in deciding on a suitable management plan.