The primary objective of this study was to determine if a pharmacist-managed anticoagulation monitoring service (AMS) improved the outcomes of patients receiving warfarin in a family practice setting and was cost effective in treating and preventing thromboembolic disorders. A retrospective chart review was performed on all patients at the University of Florida's Family Practice Residency Program who received warfarin pharmacotherapy between October 1, 1988, and December 15, 1993. The outcomes of patients followed by AMS were compared with those of a control group consisting of patients receiving warfarin but followed only by their physician. Outcomes were evaluated based on the number of thromboembolic and hemorrhagic events, as well as unplanned clinic visits, emergency room visits, and hospital admissions. Cost of hospital admissions, emergency room visits, and participation in the AMS were analyzed. During 28 person-years of treatment, control subjects sustained 12 thromboembolic events (2 pulmonary embolisms, 1 cerebrovascular accident, and 9 deep venous thromboses) and 2 minor and 5 major hemorrhagic events. The study group reported two minor hemorrhagic events during a total of 60 person-years. The control group was 20 times more likely than the study group to experience any event (rate ratio 20, 95% CI 5-87). In addition, hospitalization and emergency room charges indicated an actual cost of $119,074.95 for the control group's events. The cost to this group for 28 person-years of participation in the AMS would have been $5040.00. A potential cost avoidance of $4072.68 per person-year of follow-up may have been possible if these patients had been followed by the AMS. A pharmacist-managed AMS in a family practice setting can result in improved outcomes for patients receiving warfarin and is cost effective.