OBJECTIVE: To determine the cost-effectiveness of thrombosis prevention with Clopidogrel versus Ticlopidine in Russia, taking into account side effect such as agranulocytosis (neutropenia) using a decision analysis. METHODS: Pharmacoeconomic comparison using a decision-tree model was based on the assumption that Ticlopidine (250 mg daily) causes short-duration neutropenia in 0,8% of patients compared to 0,04 % of patients on Clopidogrel (37,5 mg daily) one month after treatment starts. The probabilities of neutropenia were derived from multi-center clinical trials of antithrombotic therapy safety. Calculated costs included cost of study drugs and direct medical costs for neutropenia treatment. A neutropenia treatment scheme was analyzed by reviewing medical charts of patients with short-duration neutropenia at the Federal Hematological Center. Effectiveness was measured by percentage reduction in spontaneous platelet aggregation (SPA) in a comparative clinical study including 70 patients with thrombophilia. Cost effectiveness ratio (CER) was defined for both drugs and incremental cost-effectiveness ratio (ICER) was determined. RESULTS: The mean costs of medication treatment were 1221 rubles (42,1$) for Clopidogrel and 795 rubles (27,4$) for Ticlopidine. The median direct medical cost for treatment of neutropenia was 28,126 rubles (969,9 $) per patient. Expected costs for antiplatelet therapy, taking into account the probability of neutropenia, was 1020 rubles (35,2 $) for Ticlopidine and 1232 rubles (42,5 $) for Clopidogrel. The CER for Clopidogrel was 19,4 rubles (0,67 $) and 20,6 rub (0,71 $) for Ticlopidine - per 1% of SPA reduction. The ICER for Clopidogrel vs. Ticlopidine was 14,5 rub (0,5 $) per 1% SPA reduction. CONCLUSION: Clopidogrel is more effective and safe than Ticlopidine. Though costs for Clopidogrel including treatment of side effects (neutropenia) were higher than for Ticlopidine, ICER shows that additional effect can be achieved for reasonable costs.