The classic treatment of chronic lymphocytic leukemia (CLL) aims at prolonging survival, without attempting to eradicate the disease. CLL commonly affects the elderly, but a small proportion of patients are less than 50 years old. In this age group a novel form of therapy, high-dose chemoradiotherapy and allogeneic bone marrow transplantation (BMT), has been used recently. Review of the literature and the IBMTR data show that 26 patients have received BMT (24 allogeneic, two syngeneic). Patients were predominantly male (20/26) with an age ranging between 21 and 49 years; 18 had advanced disease at BMT and had received multiple courses of chemotherapy to which they were considered refractory. Conditioning consisted of cyclophosphamide and fractionated total body irradiation, plus additional agents in one-third of the patients. Graft-versus-host disease (GVHD) prevention was variable. Twenty-five patients are evaluable: 12 died of early complication of BMT (GVHD, infection, haemorrhage, etc.) and only two died of CLL. The effect of BMT on the disease was evaluable in 22 patients: 19 achieved a remission, three showed persistent disease and two relapsed; 11 were alive and apparently disease-free, with follow-up between 5 and 48 months. In two of these patients molecular biology studies showed no residual disease. These results indicate that further studies of the use of BMT for selected patients with CLL appear to be justified.