A 78-year-old woman was admitted to our hospital because for pancytopenia and splenomegaly. The bone marrow examination revealed hairy cells in 11.6% of all nucleated bone marrow cells. Hairy cells were positive for tartaricresistance acid phosphatase (TRAP) staining, CD2, CD11c, CD19, CD20, sIgD, CD25, CD103 and k chain. In addition, abdominal enhanced computed tomography (CT) demonstrated splenomegaly and multiple nodular early stains in the spleen. She was diagnosed as having typical hairy cell leukemia (HCL). The patient was treated with cladribine infused continuously for 7 days at a dose of 0.09 mg/kg/day, which induced partial remission without severe adverse effects. Purine analogs such as cladribine and pentostatine are considered first-line agents for patients with HCL. Treatment with cladribine achieved a high overall response rate for patients with HCL and was safe even in elderly patients like ours. It is necessary to observe carefully the complications of severe infections, second malignancies and relapse of HCL after treatment with cladribine.