Klinefelter's syndrome is characterized by hypogonadism and infertility and commonly has an XXY karyotype. Within the population of men with this disorder, there is an increased incidence of venous thromboembolic disease. Although the precise mechanisms underlying this prothrombotic state have not been elucidated, it is thought that the increased incidence of thromboembolism is associated with a hypofibrinolytic state secondary to androgen deficiency. We present the case of a 26-year-old man with Klinefelter's syndrome who had recurrent episodes of deep venous thrombosis and pulmonary embolism while undergoing therapeutic anticoagulation. Coagulation studies were significant for the heterozygous mutations of MTHFR-677C>T and 1298A>C gene and hyperhomocystenemia. Our aim is to raise awareness of this association and discuss management for these patients.