Objectives: bone marrow transplantation is still associated with a high case-fatality rate. This study was conducted to identify the risk factors for early mortality in acute lymphocytic leukaemia patients treated with bone marrow transplantation. Methods: prospectively collected data on 76 acute lymphocytic leukaemia patients, treated with 60 mg/kg cyclophosphamide for two consecutive days, before (32 patients) or after (44 patients) total body irradiation who received an allogeneic (56 patients) or autologous (20 patients) bone marrow transplantation were considered in the multivariate analysis including fifteen potentially prognostic variables for early mortality. Results: in the entire group, patients older than 20 years had a relative risk for early mortality of 3.96 (95% confidence interval (CI): 1.33-11.76) and those with a Karnofsky Index lower than 90% had a relative risk of 5.56 (95% CI: 1.29-25). In the subgroup of allogeneic patients, those over 20 years had a relative risk of 5.17 (95% CI: 1.30-20.6); the relative risk for patients with a Karnofsky index < 90% was 10.55 (95% CI: 1.55-71.43) and 8.04 (95% CI: 43-45.07) for acute severe graft-versus-host disease. Among radiation therapy variables only dose-rate showed a trend towards better prognosis in patients treated with less than 5 cGy/min. Conclusions: in our patients and within the range of treatment variables studied, age, Karnofsky index, and graft-versus-host disease are the most important factors related with early mortality.