OBJECTIVE: A cost-avoidance model was developed to determine potential cost savings or “avoidance” that results from a drug information service (DIS) responding to drug information requests. DESIGN: Patient-specific questions received by the DIS were reviewed and evaluated. A panel determined whether a drug misadventure event may have occurred if the DIS had not been consulted. Potential outcomes from drug information requests were classified using a decision-tree model. A severity rating was then attached to each applicable request to predict potential cost savings of the DIS. RESULTS: Seventy-seven of the 570 drug information responses received in the six-week study period had assessable potential cost savings to the institution. During the study interval, potential cost savings were estimated to be $195 000. Projected to one year, potential cost savings reached $1.7 million. Of the savings noted, most were attributable to prevention of increased monitoring or additional treatment. Using a sensitivity analysis, annual potential cost savings ranged from $417 792 to $2 052 740 per year. Based on the estimated annual costs related to maintaining a DIS of $145 950, the resultant range of benefit/cost ratio is 2.9:1 to 13.2:1. CONCLUSIONS: This model demonstrates that the DIS at our institution provides potential cost savings. This model may be modified to evaluate potential cost savings in other areas of pharmacy practice.