A 78-year-old man presented with bilateral auricular and nasal chondritis and an inner ear disorder. Relapsing polychondritis (RPC) was diagnosed and corticosteroid therapy was initiated. Two years later, he developed abdominal pain and a fever. A contrast-enhanced computed tomography scan showed enhancement of the mesentery and massive ascites. The patient underwent emergency laparotomy, which revealed inflammation and thickening of the omentum. A microscopic examination of the omentum disclosed vasculitis, and corticosteroid and cyclophosphamide pulse therapies were administered. We herein report the first case of RPC complicated by pathologically proven vasculitis of the omentum, clearly indicating an association between the pathogenesis of these two conditions.