Currently, there is no universally accepted system to classify the stage IV colorectal cancer. Here, we analyze the prognostic impact of radical resection for colorectal liver metastases and propose a new staging system for stage IV colorectal cancer. A retrospective review was undertaken of 126 consecutive patients who underwent surgical treatment for colorectal liver metastases from January 1997 to January 2004. Based on the overall survival rates (Kaplan-Meier method) and surgical outcomes, we propose a new staging system for stage IV colorectal cancer. Patients were divided into two groups: patients who underwent initial hepatic resections (R0 resection) for liver metastases (group 1, n = 22), and patients who underwent palliative resection for unresectable liver metastases (group 2, n = 104). The overall survival rates in group 1 at 1, 3, and 5 years were 68.2% (15/22), 40.9% (9/22), and 18.2% (4/22), respectively. The overall survival rates in group 2 at 1, 3, and 5 years were 54.8% (57/104), 16.3% (17/104), and 0% (0/104), respectively. There was a significant difference in overall survival rates between both groups (p < 0.05). Based on the study results, we propose a new staging system where all distant metastases are grouped within stage IV and subclassified into resectable (R0 resection) and unresectable stages. Curative surgical treatment is a critical prognostic factor in colorectal liver metastases. The proposed new staging system for stage IV colorectal cancer is simple and is clinically useful to estimate the prognosis.