Vasculitis is relatively uncommon in lymphoproliferative disease and may predate the diagnosis of lymphoproliferative disease. Many vasculitides have been associated with hairy cell leukemia (HCL), including polyarteritis nodosa (PAN) and leukocytoclastic vasculitis. We herein report a case whose initial presentation was like Behçet's disease (BD) (arthritis, oral and genital ulcerations, papulopustular skin lesions) in addition to pancytopenia, but turned out to have HCL. Because of the overlap between their symptoms, like oral ulcerations, skin lesions, arthritis and constitutional findings, HCL and BD may mimic each other. We should keep in mind other reasons for vasculitis such as lymphoproliferative disease, especially whose who have hematological abnormalities such as pancytopenia.