Most patients on chronic oral anticoagulant therapy are monitored through anticoagulation clinics, or rather by assistant physicians. Our aim was to compare warfarin anticoagulated patients who were treated with usual medical care (assistant physician) with those treated routinely at an anticoagulation clinic for anticoagulation control. The later was assessed by comparing in both groups of patients the proportion of INRs within the therapeutic range, above 5.0 and below 1.5. The group treated at an anticoagulation clinic achieved better anticoagulation control (both among the patients receiving lower-range anticoagulation therapy and in the patients requiring higher-range anticoagulation therapy) than the group treated with usual medical care.