Despite the use of identical clinical trial data (Anastrazole, Tamoxifen, Alone or in Combination for the adjuvant treatment of postmenopausal women with localised hormone receptor-positive breast cancer data), not dependent on differences between countries, the outcome of 11 published cost-effectiveness analyses varied more than 20-fold. The observed wide variation in predicted life-years gained (a parameter derived from clinical trial data) demonstrates that authors used substantially different methods for handling the same data. We therefore consider it to be of utmost importance to strive for standardization of and better guidance for disease-specific modeling in economic evaluations.