Cetuximab (Erbitux) has shown activity in patients with metastatic colorectal cancer (mCRC). To evaluate the cost-effectiveness of this drug combined with irinotecan in mCRC, a model-based cost-effectiveness analysis (CEA) was performed. Data on cetuximab obtained from Medline in December 2004 and from the 2004 ASCO-meeting were analyzed for life years gained (LYG) with regard to the use of this monoclonal antibody (MAb). Norwegian prices as of January 2005 were employed. The LYG ranged between 1.7 and 2.0 years. The median cost per patient treated was calculated to 34,256 Euro to 45,764 Euro yielding a cost per LYG in the range between 205,536 Euro and 323,040 Euro. Sensitivity analysis documented price of cetuximab and survival gain to be the major factors influencing the cost-effectiveness ratio. In conclusion, the analysis indicates cetuximab to be a promising, but very expensive antibody.