Patients with bone marrow transplant may present with acute, life-threatening complications which frequently (40% of our cases) require intensive care unit treatment and result in an increased mortality (76% in this series). In an attempt to reach a more objective prognostic assessment, we have analyzed those factors related to the worst outcome in the 25 patients with bone marrow transplant admitted into our intensive care unit. Respiratory failure was the most frequent complication (72%), with an 83% mortality. Graft-versus-host disease and neutropenia led to a greater number of infectious complications with a poor outcome. Failure of more than three organ systems, septic shock and mechanical ventilation were statistically associated with mortality (p less than 0.05), and all patients who required mechanical ventilation for more than seven days or needed intensive therapy for more than 10 days died. The presence of septic shock, multisystem failure and severe neutropenia on admission should be considered as initial indicators of a poor prognosis. More than 7 days of mechanical ventilation and an intensive care unit stay of more than 10 days could be critical points in the reassessment of the intensity and prolongation of treatment.