OBJECTIVES: to calculate the impact of abacavir/lamivudine on the Mexican drug budget in 2010 and to forecast its impact over the following 5 years. METHODS: A budget impact model (BIM) of HIV infected patients was developed to evaluate the costs of abacavir/lamivudina versus emtricitabina/tenofovir and lamivudina/zidovudine from the Mexican Health Care perspective. The BIM was calculated by triangulating information derived from multiple Mexican data sources. The model is based on disease prevalence, drug acquisition cost and sales forecasting data specific to Mexico. The projected population and incidence of VIH was obtained from the literature. The (BIM) was based on two scenarios reflecting different levels of growth in the number of patient. The study was conducted from the Mexican Healthcare perspective. The average budget impact in the first 5 years (startup phase) and subsequent years (steady state) was assessed in US dollars. Future costs were discounted at 5% per recommendations for analyses in Mexico RESULTS: Increasing utilization of abacavir/lamivudine, from 5% to 60% over 5 years period resulted in an net cost saving during the initial startup phase of $ 24 millions and $ 157 millions to the steady state. These reductions translated to a total net cost saving of $ 437 millions “in 2010 dollars” over 5 years. The total direct costs decreased progressively at the end of the five-year period due to decreased acquisition drug costs. Sensitivity analyses demonstrated that the cost savings observed were maintained over a wide range of alternative values of the model parameters. CONCLUSIONS: The budget impact analysis of abacavir/lamivudine for HIV starting in 2010 shows a positive impact on the health budget because it saves costs after 2010 and produces a net benefit from the beginning of treatment. Abacavir/lamivudina led to important cost savings due to its lower drug acquisition cost.