Many patients are chronically treated with oral anticoagulants to prevent thromboembolic events. These medications are life saving but have a narrow therapeutic window, which can expose these patients to life threatening events if the International Normalized Ratio (INR) is not kept within the therapeutic window. High potential of drug-drug and drug-food interactions adds to the complexity of achieving good anticoagulation control, and knowledge of these interactions can assist in making better therapeutic decisions. OBJECTIVE: To evaluate the impact of clinical pharmacist intervention on anticoagulation control in chronic patients. METHODS: Thirty-seven chronic patients with uncontrolled anticoagulation were randomly identified from the data systems of Maccabi Health care Services. The clinical pharmacist intervention consisted of meeting the family practitioners in order to go over patient clinical charts, and sending written recommendations regarding anticoagulation control. Some of the patients were also invited to a personal meeting with the clinical pharmacist for pharmaceutical guidance, and were closely followed throughout the process. Outcome analysis was based on comparison of the last two INR results before and after the clinical pharmacist intervention, according to target INRs, matching the specific indication for anticoagulant therapy. RESULTS: Following the clinical pharmacist intervention we observed a two-fold increase in the number of patients with anticoagulation control: a 2.5 fold increase in the number of patients with anticoagulation control in the optimal range (INR between 2-3 for most of the indications and 3-4 for mechanical valve replacement), and a 1.8 fold increase in the number of patients with anticoagulation control in the tolerable range (INR between 1.8-4 for most of the indications and 2-4.25 for mechanical valve replacement). These differences were statistically significant (p = 0.018). CONCLUSION: These findings indicate that chronic patient's anticoagulation control strongly benefits from clinical pharmacist intervention. Further study is required to control for spontaneous patient improvement.