OBJECTIVES: In Mexico, two pilot studies in public hospitals assessed the economic benefit of changing from a traditional, or ward stock, drug dispensing system to a unit dose drug dispensing system. The aim of this study is to estimate the total drug savings derived from implementing a unit dose system among hospitals at IMSS. METHODS: Total and average hospital drug expenditures were estimated based on hospital drug prescriptions data base for 2009. Statistical analysis was performed to test for expenditure differences among levels of health care. The percentages of economic savings derived from previous studies were used to construct three economic benefit scenarios. These were applied to the total hospital drug expenditure. The baseline scenario was obtained from studies in Mexico that reported economic savings of 40%. A minimum and maximum scenario of 14.4% and 67.7% were obtained from international studies. The exchange rate was of $12.10 pesos per dollar. RESULTS: The total hospital drug expenditure was of USD $499.3 millions. Most of the expenditure was derived from hospitals of general and specialized level of care. Average expenditure and drug prescription dispensed were statistically higher in the specialized compared to general hospitals (p=0.0002 and p=0.00009, respectively). The total economic drug savings from the baseline scenario considering all hospitals was of USD$199.7 millions. In the maximum and minimum scenarios, the economic savings were of USD$334.5 millions and USD$71.9 millions respectively. On average savings were higher on specialized than in general hospitals. CONCLUSIONS: The estimated economic benefits, derived from implementing a unit drug dispensing system in hospitals at IMSS, was equivalent to 7.9% of the 2009 institutional budget expenditure for medical related spending in the baseline scenario. This suggests that this system can contribute to the containment of costs and the rational use of medicines on behalf of the patients and institutions.