Hairy cell leukemia-variant (HCL-V) is an extremely rare chronic B-cell lymphoproliferative disorder clinically and morphologically distinct from classic hairy cell leukemia (HCL). HCL-V is thought to represent a hybrid between prolymphocytic leukemia and HCL, the nucleus more closely resembling a prolymphocyte and the cytoplasm a hairy cell. The clinical course of HCL-V is aggressive with short survivals. Since single courses of cladribine have profound activity in HCL, inducing durable complete responses in 91% of patients, we administered cladribine to 4 patients with HCL-V over a 7-year period. During this time interval 357 patients with classic HCL received cladribine at Scripps Clinic. Each patient received cladribine at 0.1 mg/kg per day by continuous intravenous infusion for 7 days, repeated at 28-day intervals depending on response status. The 4 patients ranged in age from 28 to 70. Two presented with B-symptoms, 1 had peripheral adenopathy, and all 4 displayed massive splenomegaly. Peripheral blood counts were notable for lymphocytosis associated with mild anemia and thrombocytopenia. Only 1 of the 4 patients had received prior treatment. Peripheral blood immunophenotypic analysis revealed monoclonal B cells with expression of CD11c in 3 patients, lack of CD25 expression in 3 patients and expression of CD103 in all but 1 patient. The number of cladribine courses administered ranged from two to five. Of these 4 patients, 1 (25%) achieved a complete response and 2 (50%) partial responses, for an overall response rate of 75%. Three patients underwent splenectomy after cladribine. Cladribine is an active agent in HCL-V albeit with a lower response rate than in classic HCL. The role of other treatment modalities, such as splenectomy, interferon-alpha, and 2'-deoxycoformycin, alone or in combination with cladribine awaits further evaluation.