Prognostic scoring systems based on physiological parameters have been established in order to predict the outcome of ICU patients. It has been demonstrated that the predictive value of these scores is limited in patients following hematopoietic stem cell transplantation (HSCT). Therefore, we evaluated patients from the Düsseldorf pediatric stem cell transplantation center with regard to predisposing factors and prognostic variables for ICU treatment and outcome. Between January 1989 and December 1998, 180 HSCT have been performed. The clinical, laboratory and HSCT-related parameters such as conditioning treatment, engraftment, GVHD, infections and HSCT toxicity were prospectively recorded and retrospectively analyzed. Established pediatric scoring systems (PRISM, TISS, P-TISS) were applied. Twenty-eight patients required intensive care (16 male, 12 female, median age: 10.9 years (range: 0.4 to 18.9 years), five autologous, 13 allogeneic-related and 10 unrelated transplanted patients). Ventilator-dependent respiratory failure was the most frequent cause of admission to the ICU (n = 23). Fourteen of 28 patients were discharged from ICU, and six of 28 patients achieved a long-term survival (110 to 396 weeks). At admission to the ICU, impaired cardiovascular status, high CRP levels and presence of macroscopic bleeding were each associated with fatal outcome (P < 0.05). The Pediatric Risk of Mortality (PRISM) score was not prognostically significant at the 0.05 level. Long-term survival after discharge from the ICU correlated with HSCT-related parameters such as the type of transplant and severity of GVHD (P = 0.002). By introduction of HSCT related parameters such as severity of GVHD (grade 2: 2 points; grade >2: 4 points), CRP-level (>10 mg/dl: 4 points), and presence of macroscopic bleeding (4 points) into the PRISM score a new oncological PRISM ('O-PRISM') score was established. This score significantly correlated with the risk of mortality in the ICU (P = 0.01). In conclusion, the new O-PRISM score accurately characterizes the clinical situation of children requiring ICU treatment following HSCT. It distinguishes more appropriately between success and failure of ICU treatment following HSCT than the standard prognostic scores. It needs to be evaluated in future prospective studies of critically ill children after HSCT. Bone Marrow Transplantation (2000).