OBJECTIVES Studies in Mexico have shown that the health expenditure attributed to antirretroviral treatments for naïve and experimented patients is high. This has an impact on the national budget of the public health institutions, especially for units from the Ministry of Health which deal with the largest number of HIV/AIDS cases in the country. The objective of this analysis was to estimate the financial impact of increasing the availability of atazanavir for the treatment of patients with HIV/AIDS in the MoH institutions. METHODS A budgetary impact model based on epidemiological data, treatment costs and market uptake for four proteasa inhibitors (PI) in a time horizon of five years was developed. A baseline scenario, where the current PIs market distribution remains the same, was compared with a scenario where atazanavir availability is increased. RESULTS The estimated numbers of infected HIV/AIDS subjects will grow around 53.48% in the next five years. As a result, more resources will be needed to face the increasing burden of the disease. The comparisons between the two scenarios show that the estimated budget impact related to the acquisition of PI is cost-saving. The estimated savings in 2009 are of US$1.168 million increasing 3.4 times during the five years period. Savings from the treatment of main side effects such as, diarrhea and cholesterol lowering intervention are also observed (US$ 12,777 and US$17,861 in 2009 respectively). CONCLUSIONS An increase in the utilization of atazanavir represents a good clinical and economic option for the Mexican MoH in the short and long run. The highest impact in the budget is produced mainly by the pharmacological costs. However, budget savings are also derived from the reduction of treatment costs side effects such as diarrhea and hypercholesterolemia.