The report dealt with a 64 years-old female presented with massive splenomegaly, anemia and peripheral lymphocytosis with circulating hairy cells. The clinical and laboratory features prompted a clinical diagnosis of hairy cell leukemia. The distinctive splenic changes made the diagnosis of hairy cell leukemia revised to a malignant lymphoma, well differentiated lymphocytic type with leukemic features. Diagnostic features of hairy cell leukemia were reviewed in detail. Clinical and hematologic diagnosis of hairy cell leukemia should be confirmed by histologic examination.