The O-PRISM score was introduced for risk assessment in children transferred to intensive care following BMT. The aim of this study is to determine the prognostic value of a serial evaluation of the O-PRISM score. Ninety-three children, 58 allogeneic-related and 35 unrelated BMT, were evaluated. At weekly intervals, the O-PRISM was calculated based on the standard PRISM score and the three additional variables CRP, GVHD and hemorrhage. Overall survival was 0.51 +/- 0.05 (48/93 patients). Seventeen children died of recurrent disease and 28 of BMT-related complications. High O-PRISM scores significantly correlated with adverse outcome. The relative risks of DOC of patients with scores > or =10 compared to patients with lower scores were: day 0: 3.9 (95% confidence-interval: 1.1-13.7, P = 0.02), day 7: 2.0 (0.7-6.2, P = 0.20), day 14: 5.2 (1.9-14.0, P = 0.001), day 21: 5.6 (1.9-16.5, P = 0.001), day 28: 11.5 (3.8-100.9, P < 0.001), day 35: 7.3 (1.9-27.7, P = 0.001). As early as day 0, children with scores > or =10 points showed a higher cumulative incidence of DOC than patients with lower scores (0.69 +/- 0.15 vs 0.27 +/- 0.05, P = 0.02). The O-PRISM score represents a useful clinical parameter for serial risk assessment following BMT. As it indicates fatal events early, it may be helpful for parent information and even more for the early establishment of intensified supportive treatment. The O-PRISM score may therefore be a valuable parameter for the evaluation of different strategies for BMT and supportive treatment.