Physicians' outcome predictions probably influence their treatment decisions in the ICU. The importance and accuracy of these predictions, however, are poorly defined. We asked 20 ICU physicians to rate the importance of 14 factors used for treatment decisions. Expected functional outcome rated highest. However, physicians' predictions of patient outcome, specifically survival and need for professional nursing care 45 days after ICU admission, had variable accuracy. For example, physicians predicted death for only 41% of adults who died, but survival for 87% of adult survivors. Predictions of survivors' need for professional nursing care proved 100% correct for children after heart surgery, but only 58% to 73% correct for other patient groups. These inaccuracies pose an important ethical question: what is the proper role of outcome predictions in ICU decision-making? We believe outcome predictions have an important role when they are proven accurate and used within the bounds of loyalty to the patients and respect for his wishes.