Although the coexistence of hairy cell leukemia with sarcoidosis has been reported in a few cases in the literature, in our case the patient had been diagnosed and followed about 10 years with sarcoidosis and massive splenomegaly. It has been demonstrated that T helper 1 cells exist in organs influenced by sarcoidosis. These cells produce IL-2 and IFN-γ and induce a nonspecific inflammatory response and granuloma formation. Also these cytokines may play a role in the development of hairy cell leukemia.Key words: hairy cell leukemia - sarcoidosis - massive splenomegaly.