Despite encouraging results seen following bone marrow transplantation (BMT), it has been observed that once these patients become critically ill and require medical intensive care unit (MICU) admission, the chances of survival are poor. We hypothesized that while mechanical ventilation would be an important predictor for death in the MICU, those patients not requiring mechanical ventilation could be successfully discharged from the MICU. The records of 36 patients with 43 admissions to the MICU following BMT were analyzed. Of these admissions, 33 (76.7 percent) patients had allogeneic and 10 (23.3 percent) had autologous transplants, respectively. Overall, 14 (32.6 percent) of the admissions resulted in a satisfactory discharge from the MICU. There was no significant difference in the survival rates between those patients undergoing allogeneic or autologous transplantations, 11 (33.3 percent) vs 3 (30.0 percent), respectively. Twenty-seven (62.8 percent) of the admissions resulted in mechanical ventilation and were performed in 20 (66.7 percent) patients with allogeneic BMTs and 7 (70.0 percent) patients with autologous BMTs, which was not significantly different. The survival rate for those requiring mechanical ventilation was significantly less than for those not mechanically ventilated during their MICU stay, 1 (3.7 percent) vs 13 (81.3 percent), respectively (p < 0.001). Those patients who did not survive their MICU stay had a significantly higher mean APACHE II score of 21.2 +/- 4.7 than the survivors' score of 15.8 +/- 3.8 (p < 0.001). The average length of stay for the survivors was 4.4 + 3.0 days, which was significantly less than the 17.8 +/- 24.0 days for those patients not surviving (p < 0.001). These data indicate that admission to the MICU may result in a beneficial outcome for critically ill patients with BMTs, but for those requiring mechanical ventilation due to respiratory failure, the chances of survival are poor. This information may be useful for providing patients with BMTs and their families with realistic estimates of prognosis prior to transfer to the MICU and mechanical ventilation.