We herein report a 34-year-old man who was investigated for severe abdominal pain. Portal vein thrombosis (PVT) and mesenteric vein thrombosis (MVT) were diagnosed. An association with two predisposing factors for thrombosis was noted: (1) heterozygous factor II 20210G/A mutation and (2) homozygous methylenetetrahydrofolate reductase (MTHFR) 677C/T mutation with hyperhomocysteinemia. Our case is of particular interest because the patient reported herein, is homozygote for the MTHFR 677C/T mutation, while the only two other cases reported in the literature with similar gene mutations, were heterozygotes for the mutation.