We performed a retrospective study on the use of cetuximab or panitumumab alone in patients with KRAS wild-type metastatic colorectal cancer between November 2008 and February 2012. Twenty-two patients were analyzed and classified as PS 0/1 (good PS group)and PS 2/3/4 (poor PS group)with 11 patients in each group. The response rate, disease control rate, median progression-free survival, and median overall survival were 9%, 73%, 5.1 months (95%confidence interval[CI]: 1.5-8.7), and 16 months (95% CI: 8.8-24), respectively, in the good PS group, and the corresponding values in the poor PS group were 0%, 18%, 0.7 months (95% CI: 0.3-1.0), and 1.5 months (95% CI: 0.7-2.4). Grade 3 or 4 adverse events were skin toxicities (2 patients with grade 3 toxicities), panitumumab-related interstitial lung disease (1 patient with grade 4 toxicity), and cetuximab infusion-related reaction (1 patient with grade 4 toxicity). No treatment-related deaths were observed. In conclusion, the efficacy and safety of cetuximab or panitumumab monotherapy in patients with a good PS in our study were similar to those reported in previous clinical trials, whereas patients with a poor PS showed poorer outcomes.