OBJECTIVES: Pharmacist-managed anticoagulation clinics (ACC) have been proven to provide positive outcomes in both overseas and local tertiary settings as part of a health care team in caring for patients on warfarin therapy. However, currently, there is no published study on the effectiveness of pharmacist-managed ACC in the primary care settings in Singapore. Therefore, the primary objectives of this study were to determine the effectiveness of pharmacist-managed ACC in maintaining INR within the therapeutic range, and their associations with patient demographics.  The secondary objective was to examine the incidence of warfarin-related adverse effects. METHODS: This was a retrospective, time-series study conducted in nine outpatient primary care clinics in Singapore from September to December 2009.  All patients aged ≥ 21 years with at least three visits with the ACC pharmacists within the first 12 months of physician referral were included in this study. Patient demographics and clinical outcomes, such as INR and incidence of warfarin-related adverse events, were collected at first visit to ACC and at every 4-month interval for a total of 12 months. RESULTS: A total of 269 patients were under the care of ACC pharmacists from April 2008 to May 2009, and of which 82 (30%) met the inclusion criteria. INR was maintained at therapeutic range throughout the 12-month period with minimal fluctuations between each visit (p = 0.621). There was no association between INR and patient demographics except for intake of vitamins, supplements and herbal medications (p = 0.006) and change in medications (p = 0.039) at the 12th month. Documented warfarin-related adverse events included gingival bleeds (1; 1%), leg cramps (5; 6%), and swells (5; 6%). CONCLUSIONS: Pharmacist-managed ACC in the primary care settings in Singapore were effective in maintaining INR within the therapeutic range.  The service also minimized the frequency of adverse events commonly associated with warfarin therapy.