The medical records of 77 patients with hematologic malignancy who were admitted to a medical intensive care unit over a 21-month period were reviewed. The overall hospital mortality rate was 80 percent. Sixteen patients (21 percent) were discharged from the intensive care unit but eventually died in the hospital. The cause of death was the result of a new problem in only three of these 16 patients. Hypotension (shock) and acute respiratory failure were the reasons prompting admission to the intensive care unit in 75 percent, but death in the intensive care unit was almost always the result of intractable hypotension rather than refractory hypoxemia. Only four of 52 patients who required mechanical ventilation left the hospital. In all four, the duration of ventilatory support was less than five days and the cause of respiratory failure was noninfectious in nature. Factors such as congestive heart failure, leukopenia, and abnormalities in mental status modified the hospital course, but did not alter outcome once prolonged mechanical ventilation became necessary. The data suggest that once acute respiratory failure develops in patients with lymphoma or leukemia, presumably as a result of infection, and mechanical ventilation for more than a relatively brief period is required, the prognosis is uniformly grim. Decisions to limit aggressive therapies is subsets of intensive care patients such as these should be aided by data that show a lack of precedent for meaningful recovery.