Although Behçet's disease (BD) is a multisystem disorder of unknown causes, both genetic and environmental factors have been suggested. This is the second reported case of monozygotic twins concordant for Behçet's disease and the first such report of intestinal Behçet's disease. Patient 1 was a 17-year-old man with fever, recurrent oral aphthae, and skin eruptions. He developed hematochezia and was given corticosteroid empirically. One month after he was discharged, he again developed oral ulcerations, fever, and hematochezia. Colonoscopy was performed again, showing aphthous ulcerations in the entire colon, and deep oval ulcers with marginal elevation around the ileocecal valve, which are characteristics of intestinal Behçet's disease. He was treated with colchicine and azathioprine in combination with salazosulfapyridine (SASP) and prednisolone (PSL) and achieved remission. Patient 2 was the twin brother of patient 1. He was admitted because of oral aphthous ulcerations, fever, pustules on his face and body, and genital ulcers. Two weeks later he developed hematochezia. Colonoscopic and barium enema findings were similar to those of his brother. SASP, PSL, colchicines, and azathioprine were also required to achieve remission. Both of the patients were diagnosed with intestinal Behçet's disease. Their monozygosity was confirmed by detailed genetic typing, and HLA-B51 was negative.