To evaluate the prognostic significance of mechanical ventilation for outcome of intensive care therapy for pulmonary complications after allogeneic bone marrow transplantation (aBMT) we analysed the clinical course of ten patients requiring intubation and mechanical ventilation after aBMT for pulmonary complications. Ten out of eighty-five patients (12%) undergoing aBMT between 1989 and 1995 required mechanical ventilation for pulmonary complications at our university adult intensive care unit (ICU). Ventilation could be discontinued in four patients after pulmonary function improved. Three of these patients are long-term survivors after two to five years (median 37 months) of follow-up. Significant differences between the two groups of survivors (n = 4 patients) and non-survivors (n = 6 patients) which could have an impact on prognosis exist for graft-versus-host-disease (GvHD), (p < 0.04) and the time between aBMT and intubation (p < 0.05). There were no differences for age (median: 36 and 34 years of age respectively), laboratory values, duration of mechanical ventilation (median: 7 days for both groups) and APACHE-scores. In survivors, mechanical ventilation became necessary because of atelectasis or obstruction by mucositis in two cases, septicemia with concomitant ARDS in one case and bacterial pneumonia in one case. In non-survivors, pulmonary complications were caused by infections. Causes of death were septicemia or septic shock in five cases and GvHD-induced bronchiolitis obliterans in one case. In conclusion patients at risk for fatal outcome after intensive-care therapy for pulmonary complications following aBMT show a higher degree of GvHD, more infectious complications and a later onset of ventilation after aBMT. With an overall longterm-survival of 3 out of 10 patients, mechanical ventilation seems to be live-saving in a selected subset of patients.