OBJECTIVES: To identify the cost effectiveness ratio of Vemurafenib in the treatment of patients of the public health care institutions in Mexico, with BRAF positive mutation (BRFAF +) metastatic or advanced melanoma, compared with dacarbazina and temozolomide. METHODS: A Markov model was developed with monthly cycles, with 4 health states: clinical benefit, stable disease, disease progression and death, considering the adverse events as transitory stages, during a 5 year time horizon. A cost effectiveness analysis was developed, where the transition probabilities between the different health’s states considered, are the basis to estimate how many life years (LY) the patients will achieve with the different treatment alternatives. The costing method used in this study is the direct medical costs, expressed in US dollars. RESULTS: In the pharmacoeconomic analysis, Vemurafenib was the most effective treatment  producing a mean of 2.15 LY per patient during the 5 year time horizon, 1.17 additional LY to those produced by dacarbazine (.98 LY) or temozolomide (0.98 LY). This shows that Vemurafenib is the most effective alternative for this patient due the effectiveness is 2.2 times higher compared to dacarbazine and temozolomide. CONCLUSIONS: Given the current worldwide discussion regarding the cost-effectiveness (CE) of orphan drugs, is considered necessary to evaluate these drugs under a different criteria that those used for drugs that are not orphans. So patients, who have rare and deadly diseases, can have the opportunity to live longer and better