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Background Stage IV colorectal cancer encompasses various clinical conditions. The differences in prognosis after surgery between different metastatic organs have not been fully investigated. Objective This study aimed to assess prognostic significance in peritoneal metastasis in R0 resected stage IV colorectal cancer. Design We conducted a multicenter retrospective study of patients with R0 resected stage IV colorectal cancer; they were categorized into 3 groups according to the number and location of metastatic organs, including single-organ metastasis in the peritoneum, single-organ metastasis at sites except the peritoneum, and multiple-organ metastases. Settings This study used data accumulated by the Japanese Study Group for Postoperative Follow-Up of Colorectal Cancer. Patients A total of 1133 patients with R0 resected stage IV colorectal cancer were registered retrospectively between 1997 and 2007 in 20 referral hospitals. Main outcome measures Cancer-specific survival rates between the groups were measured. Results The median cancer-specific survival of the single-organ metastasis in the peritoneum group was considerably shorter than that of the single-organ metastasis at a site other than the peritoneum group and was almost comparable to that of the multiple-organ metastases group (3.41 years, 6.20 years, and 2.99 years). In a multivariate analysis of cancer-specific survival, peritoneal dissemination was confirmed as an independent prognostic factor of survival. The median postrecurrence survival of single-organ metastasis in the peritoneum group was considerably shorter than that of the single-organ metastasis at a site other than the peritoneum group. Approximately half of the patients who experienced recurrence of single-organ metastasis in the peritoneum experienced peritoneal recurrence. Limitations This was a retrospective, population-based study that requires a prospective design to validate its conclusions. Conclusions Peritoneal metastasis of colorectal cancer frequently recurred in the peritoneum even after R0 resection. The cancer-specific survival of the single-organ metastasis in the peritoneum group was as poor as that of the multiple-organ metastases group. See Video Abstract at http://links.lww.com/DCR/A398.