We have summarised published Norwegian and international studies of the cost-effectiveness of cetuximab in combination with irinotecan as third line treatment for patients with metastatic colorectal cancer. The present alternative to such treatment is supportive care. The estimated number of patients with metastatic colorectal cancer eligible for treatment with cetuximab + irinotecan as third line therapy is 70. Four studies covering the cost-effectiveness of cetuximab + irinotecan were identified, two of which satisfied the inclusion criteria. A considerable problem for all four studies was the lack of effectiveness data based on a direct comparisons of cetuximab + irinotecan vs. supportive care or absence of third line therapy. The two included studies were from Norway; Norum 2006, and the UK; Starling . 2007. Calculation of incremental effect was in these studies based on different forms of indirect comparisons. Norum estimated the benefit associated with cetuximab + irinotecan relative to absence of third line treatment to be between 1.7 and 2 life months gained in terms of median survival. The cost per life year gained was estimated to be between 1.7 and 2.6 million Norwegian kroner. This is however, based on the difference in effect between cetuximab + irinotecan and cetuximab monotherapy. In Starling , treatment with cetuximab + irinotecan was assessed relative to active/best supportive care (which may involve active chemotherapy). The results indicated that treatment with cetuximab + irinotecan was associated with an increase in average survival of 5.3 months, and 0,33 QALYs gained. The cost per life year gained was estimated to 508 000 Norwegian kroner. The cost per QALY gained was somewhat higher, at 681 000 Norwegian kroner. In the two studies which were not included, the authors stated that they did not wish to construct a health economic model when there is a lack of direct evidence with respect to comparing the effectiveness of cetuximab + irinotecan versus ASC/BSC or the absence of third line treatment. The evidence base regarding the cost-effectiveness of cetuximab is, at the time of writing, weak, particularly with regard to relevant efficacy data. Treatment with cetuximab + irinotecan as third-line therapy would not be cost-effective in light of suggested thresholds for costs for an extra QALY/year in good health. However, such a view would not account for the notion that societal preferences regarding treatment of this patient group might differ from preference for other interventions. The cost-effectiveness of cetuximab as first- or second-line treatment has not been considered here as no health economic evaluations were found for these stages.