OBJECTIVE: This study evaluated the effects of pharmacist-managed anticoagulation monitoring services on the clinical and economic outcomes of patients prescribed warfarin therapy. METHODS: A retrospective chart review was conducted for patients newly initiated with warfarin therapy between November 1997 and April 1998. Patients used warfarin for a minimum of 2 months and were followed for either one-year post-initiation of warfarin usage or until discontinuation of warfarin therapy, whichever was earlier. Comparisons were made between the group of patients receiving anticoagulation monitoring through usual medical care (UMC) by their physician ("UMC group") and those patients enrolled in the pharmacist-managed anticoagulation clinic ("AC patients"). Outcome measures for the two groups include anticoagulation control, incidence of warfarin adverse effects or recurrent thromboembolic disorder, and economic evaluation for inpatient and outpatient health care services utilized. RESULTS: Complete data for 63 UMC patients (625 patient-months) and 18 AC patients (232 patient-months) indicate that AC patients had better anticoagulation control than UMC patients (51% of INRs within target range versus 41%, respectively). However, AC patients experienced more frequent minor recurrences (events not requiring hospitalization) of thromboembolic disorders or bleeding associated with warfarin (0.11 events per AC patient-month versus 0.08 events per UMC patient-month). The incidence of complications that necessitated hospitalization was similar between the two groups. The estimated annual inpatient cost of treating the complications associated with anticoagulant therapy was $168 less per AC patient but equivalent for both groups for outpatient services ($348 annually). Inpatient and outpatient charges for all medical claims for AC patients were less than half that found for UMC patients ($241 and $405 per patient-month versus $501 and $878 per patient-month, respectively). CONCLUSION: Although treatment-related complications can still occur, pharmacist-managed anticoagulation monitoring services provided a better means of maintaining anticoagulation control and reducing medical care costs for patients on warfarin therapy.