Leg ulcers may occur due to many autoimmune, hereditary, inflammatory, and infectious causes including venous, arterial, and neuropathic ulcers. Hyperhomocysteinemia is a metabolic disorder caused by various enzyme defects in methionine metabolism. The most common cause is methylenetetrahydrofolatreductase (MTHFR) enzyme gene mutations. Hyperhomocysteinemia is an independent risk factor for deep vein thrombosis and peripheral arterial disease. The effects of endothelial cell damage on smooth muscle hypertrophy, platelet aggregation, coagulation, and fibrinolysis cause atherogenesis and thrombosis, leading to venous and arterial lower extremity ulcers. In this article, we report the case of a 47-year-old male patient who was admitted to our clinic due to painful leg ulcers that started 1 year ago. He had a history of vena cava inferior thrombosis, deep vein thrombosis, and 40 pack-year smoking. Histopathological examination of punch biopsy taken from ulcerative lesion showed intense inflammatory infiltration in the middle dermis, erythrocyte extravasation, leukocytoclasia, and thrombus formation in a small diameter venule lumen. There were nonspecific findings in direct immunofluorescence examination. He was found as having MTHFR C677T homozygote and plasminogen activator inhibitor-1 4G/5G heterozygote gene mutation with high homocysteine level of 22.90 mu mol/L, and he was diagnosed as hyperhomocysteinemia. He was recommended to quit smoking because it triggered thrombosis in hyperhomocysteinemia. Herein, we present a case of hyperhomocysteinemia due to MTHFR mutation, which is one of the rare hereditary thrombophilia causes.