Objective: We aimed to investigate the frequency of Factor V Leiden mutation among venous thromboembolism patients admitted to our center and we intended to detect the risk of thromboembolism in mutation carrying family members by genetic counseling. Material and Methods: In this study a total of 72 patients with venous thrombosis admitted to Haydarpasa Numune Research and Training Hospital, Genetic Diseases Diagnosis Center between January and August in 2008 were investigated for Factor V Leiden mutation. Patients were informed and their consents were obtained. All of the patients had pedigree analysis and affected family members were investigated. Genomic DNA was isolated from peripheral blood using proteinase K digestion method. Factor V gene, covering 1691. nucleotide region was amplified with appropriate oligonucleotide primers and products were analyzed with RFLP method. Results: Twenty two percent (n= 16) of the our patients had chronic renal disease with fistula problems, 17% (n= 12) had deep venous thrombosis, 32% (n= 23) had cerebrovascular accidents and the remaining 29% (n= 21) had recurrent abortus. In our center, the molecular genetic analysis for Factor V Leiden mutation 59 revealed that had a normal allele. Among the remaining 13 patients, 4 of them were detected as homozygote and 9 of them as heterozygote for the mutation. Mutation carrier status was found 18% among all patients. The risk of having at least one family member with thrombosis was 23% in mutation carrying patients' family. Conclusion; As a result of this study, the importance of molecular genetic analysis and genetic counseling for the patients admitted to our center has been demonstrated. It could be possible to detect the target risk population through investigation of thrombophilia in a larger study group.