Objective: The increased risk for thrombosis is known as hypercoagulability or thrombophilia. In our study, we aimed to determine the frequency of the identified defects for thrombophilia in patients with central venous thrombosis aged under 50 years and to compare results with the findings in the current literature. Materials and Methods: Forty-three patients (16-50 years old) were retrospectively evaluated. Thrombophilia investigation included determinations of protein C, protein S, antithrombin, and activated protein C resistance, factor V Leiden (FVL), prothrombin 20210A (PT 20210) and methylene tetrahydrofolate reductase (MTHFR) C677T mutations, antiphospholipid antibodies (APA), factor VIII levels, and homocysteine levels. Results: We detected a single thrombophilic defect in 67.4%, two defects in 27.9% and three defects in 4.7% of our patients. The most common thrombophilic defect was mutation in the MTHFR gene (41.8%), and this was followed by the FVL mutation (34.9%). Conclusion: Since the prevalence of individual thrombophilic defects varies in each population, ethnic group and geographical location, screening for thrombophilic defects in patients presenting with cerebral venous thrombosis should primarily investigate the most frequent thrombophilia risk factors. (Turk J Hematol 2010; 27: 162-7) Key words: Cerebral venous thrombosis, thrombophilia, thrombophilic defects Received: October 4, 2009 Accepted: March 22, 2010 Özet Amaç: Tromboz riskinin artması hiperkoagulabilite ya da trombofili olarak bilinmektedir. Çalışmamızda, serebral venöz tromboz gelişen ve trombofilik defekt saptanan 50 yaş ve altı hastalarımızda tespit edilen trombofilik defektleri, sıklığını değerlendirmek ve literatür bilgileriyle karşılaştırmak amaçlanmıştır.