We have undertaken a model based analysis of the cost effectiveness of bevacizumab for first line treatment of metastatic colorectal cancer in Norway. We have investigated the effect of adding bevacizumab to standard chemotherapy. The analysis does have a considerable uncertainty, and the results should therefore be interpreted carefully. In our main calculation we have estimated the cost per life year gained, by adding bevacizumab to standard first line treatment with irinotecan or oxaliplatin based chemotherapy, to 668 000 NOK and 549 000 NOK – seen from a health care and a societal perspective, respectively. The cost per life year gained is, independent of perspective, higher than several suggested pragmatic thresholds for assessment of cost effectiveness in the health care sector. The main part of the incremental costs by adding bevacizumab to standard treatment is related to the aquisition cost of bevacizumab. The health effect estimate, measured as life year gained, is 0,41 year (undiscounted) in our main calculation. The incremental cost per average patient is 247 000 NOK and 203 000 NOK, in the health care and societal perspective, respectively. The sensitivity analysis shows that the cost per life year gained is very dependant on the health effect estimate, dependant on the bevacizumab price and the assumed number of bevacizumab treatment cycles, but to a lesser extent dependant of non drug costs, like treatment administration and evaluation. The uncertainty of the treatment effect estimate is due to the estimate being derived from only one relevant clinical study. The study has limited period of follow up (11-31 months) and compares bevacizumab with another, and presumably less effective irinotecan regime, than what is standard in Norway. Also similar analyses from Denmark and England indicate relatively high costs per life year gained, of bevacizumab for colorectal cancer. The evidence basis for health economic evaluations of bevacizumab in Norway (and other countries) would have been considerably better if there thad been more relevant clinical studies, with longer follow up, and where bevacizumab where compared with standard treatment in Norway (and other countries). In line with analyses from Denmark and England, the Norwegian analysis indicates that adding bevacizumab to standard irinotecan based first line treatment for metastatic colorectal cancer in average leads to 0,41 life years gained, and that the costs for this gain is higher than several suggested pragmatic thresholds for assessment of cost effectiveness in the health care sector. There are however no clear decisions on what thresholds should apply for cost effective treatment in Norway, and if these thresholds are independent of disease and patient life situation. Thus, we have no basis for concluding that adding bevacizumab to standard first line treatment of metastatic colorectal cancer is cost effective. The calculations are however uncertain. Especially, the treatment effect estimate is uncertain, being based on only one clinical study, with a presumably sub optimal irinotecan regime and limited follow up period.