OBJECTIVE: A cost avoidance model was developed to determine potential cost savings (PCS) of a drug information service (DIS) that’s results from answering a drug information request. DESIGN: Patient-specific questions received by the drug information service were reviewed and evaluated. A panel determined whether or not appropriate drug therapy would have been employed if the DIS had not been consulted. Potential outcomes of drug information requests were classified using a decision-tree model. A severity rating with potential cost avoidance was then attached to each applicable request to predict PCS of the DIS. RESULTS: Seventy-seven of the 570 drug information responses in the six-week study period had assessable PCS to the institution. During the study interval, PCS were estimated to be $196, 000. Projected to one year, PCS reached #1.7 million. Of the savings noted, most were in the categories of increased monitoring and additional treatment. Annual PCS using a sensitivity analysis ranged from $423,601 to $1,922,560 per year. CONCLUSIONS: This model demonstrates that the DIS at our institution does provide substantial cost avoidance. This model may be modified to evaluate PCS in other areas of pharmacy practice.