Purpose. Report descriptive outcome measures related to the quality of pharmacist-managed anticoagulation care with warfarin in patients with breast cancer since the formation of the anticoagulation management service (AMS).Methods. Retrospective review of 145 patients with breast cancer (median age 54 years) receiving warfarin therapy for venous thromboembolism (VTE) managed by the pharmacist-run AMS between 1998 and 2005.Results. The median time followed by the AMS was 151 days. Fifty three percent (n = 1651) of total lab draws (n = 3129) were within the target therapeutic INR range 2–3. Recurrent thrombosis occurred in 4.1% of patients. Minor bleeding occurred in 18.6% of patients and major bleeding occurred in three patients (2.1%, gastrointestinal, intra-abdominal, and subdural hematoma).Conclusion. To date, this is the largest known published database of cancer patients receiving anticoagulation in a pharmacist-managed anticoagulation service. Recurrent VTE rates, major and minor bleeding rates, and percentage of time spent within the therapeutic range are slightly different in our patient population compared to an oncology population receiving warfarin and a non-oncology population with warfarin managed by AMS. Oral anticoagulation with warfarin is an effective, albeit complicated, treatment for venous thromboembolism in the oncology population. Although low-molecular weight heparin (LMWH) therapy is now the preferred treatment for thrombosis in malignancy, warfarin is still relevant in patients who are unable to receive treatment with LMWH. This report provides valuable information supporting coordinated anticoagulation therapy with a pharmacist-managed service in a breast cancer-specific population, and contributes to the growing data supporting the challenging nature of maintaining warfarin anticoagulation in patients with cancer.