Objective: Psoriasis is a dermatological disease with major consequences on the quality of life of patients. Biological treatments for this disease have an effectiveness which is equivalent to that of conventional drugs with fewer side effects. The objective of this analysis was to evaluate the cost-effectiveness of the treatment for moderate to severe psoriasis from an institutional perspective in Mexico. Methods: To compare the cost and the effectiveness, a decision tree model was structured with a temporary horizon of 12 weeks. Only costs per drug were considered for this analysis, as the rest of the costs are similar for institutional buyers. Comparators: infliximab 5mg/kg given at weeks 0, 2, and 6; etanercept 25mg twice weekly, etanercept 50mg twice weekly and efalizumab 1mg/kg weekly. Effectiveness measure: percentage of patients with a PASI 75 (Psoriasis Area and Severity Index) response. Costs were estimated using prices of 2007, and an exchange rate of x pesos/dollar was used. Costs were estimated using 2007 prices and are expressed in U.S. dollars (exchange rate of 10.93 pesos per U.S. dollar). Results: Costs expected per treatment type are: $6987 infliximab, $6422.70 efalizumab, $5555.40 etanercept 50mg and $2777.70 etanercept 25mg. The percentage of patients achieving a PASI 75 response per treatment type is: 84% for infliximab, 49% for etanercept 50mg, 33% for etanercept 25mg and 28% for efalizumab. The following ICERs were obtained for infliximab: $1007.70 vs. efalizumab, $8253.50 vs. etanercept 25mg and $4090.50 vs. etanercept 50mg. In the three cases, ICERs are less than three times the GDP per capita in Mexico. Conclusion: Infliximab is a cost-effective drug for the treatment of moderate to severe psoriasis.