Recent advances in chemotherapy for stage IV colorectal cancer have improved clinical outcome. According to the seventh edition of the TNM classification of colorectal cancer, stage IV is classified into stage IVA and stage IVB. In this study, we assessed the clinical validity of this classification as a prognostic factor. The subjects were 170 patients with stage IV colorectal cancer(stage IVA, n=78; stage IVB, n=92)treated between January 2006 and December 2011 at our institute. Of 92 patients with stage IVB, peritoneal carcinomatosis alone was recognized in 21 patients. The median survival periods for patients with stage IVA and IVB were 29.2 and 16.1 months, respectively( p=0.13). The median survival period for patients with peritoneal carcinomatosis alone was 37.6 months, and there was no difference between survival in patients with stage IVA and those with peritoneal carcinomatosis alone. Our present results suggest that it may be reasonable and useful to classify peritoneal carcinomatosis alone into stage IVA instead of stage IVB in clinical practice.