The continuation of trastuzumab beyond progression in combination with capecitabine as secondary chemotherapy for HER2-positive metastatic breast cancer (MBC) prolongs progression-free survival without a substantial increase in toxicity.; A Markov cohort simulation was used to follow the clinical course of typical patients with MBC. Information on response rates and major adverse effects was derived, and transition probabilities were estimated, based on the results of the Breast International Group 03-05 clinical trial. Direct costs were assessed from the perspective of the Swiss health care system.; The addition of trastuzumab to capecitabine is estimated to cost on average an additional of ?33,980 and to yield a gain of 0.35 quality-adjusted life years (QALYs), resulting in an incremental cost-effectiveness ratio of ?98,329/QALYs gained. Probabilistic sensitivity analysis showed that the willingness-to-pay threshold of ?60,000/QALY was reached in 12% of cases.; The addition of trastuzumab to capecitabine in MBC patients is more expensive than what is typically regarded as cost-effective but falls within the value ranges found for established regimens in the treatment of MBC.