OBJECTIVES: To develop a cost-effectiveness analysis to compare docetaxel vs docetaxel+trastuzumab as first line therapy in the treatment of patients with advanced or metastatic breast cancer HERneu+ from the public health system Perspective in Mexico. METHODS: A markov model was built in order to simulate the clinic course of a cohort of patients with metastatic breast cancer HERneu+ in treatment with docetaxel vs docetaxel+trastuzumab as first line treatment. The model include three health states (without progression, progression and death), with a 12- month following. Conceptual frame and clinical course was based on literature review and controlled clinical trials. In order to define resources and procedures to set costs, a literature search for economic evaluation and different disease management alternatives was done. The drugs costs were obtained from the costs of purchasing published by the Mexican Institute of Social Security and included diagnosis, treatment, following and medical support. The clinical benefit of the treatment is to be determined by Progression-Free Survival (PFS). RESULTS: Using docetaxel+trastuzumab 49.1% of patients were free of progression and 25.6% of those who used only docetaxel during the 12 months of management; In other words, to maintain a patient free of progression at 12 moths is necessary to treat 2.04 and 3.91 patients with docetaxel+trastuzumab and docetaxel respectively. The expected cost with docetaxel+trastuzumab is US$32,460.87 and with docetaxel US$22,735.74. The cost to maintain a patient free of progression at 12 moths is US$66,085.92 and US$88,899.50 (mean cost effectiveness ratio) and the ICER is US$41,305. CONCLUSIONS: Results show that docetaxel+trastuzumab is a cost effective therapy when comparing with docetaxel in first line therapy for patients with metastatic breast cancer.