HIV infection and AIDS are common diagnoses in many intensive care units (ICUs) in the United States. Although Pneumocystis carinii currently represents only one quarter of all diagnoses for which HIV-infected persons are admitted to the ICU, it is the disease with the most clinically applicable outcome data and, therefore, is a model for ethical decision-making regarding patients with HIV infection in the ICU. Despite advances in diagnosis and treatment of HIV-related P. carinii, recent studies show that only 20% to 25% of the patients with acute respiratory failure survive to hospital discharge. Although many clinical markers correlate with survival, none of the individual markers or prediction scoring systems have the accuracy needed in clinical practice. One goal of predicting outcome in the ICU is to aid both the patient and the physician in making decisions about when to pursue aggressive therapy and when to withhold or withdraw such therapy. Because our ability to predict outcome is limited, advance directives and communication with patients and families about end-of-life medical care are of utmost importance. Even though it is not always possible for patients to predict, in advance, what they would want done in various hypothetical health care scenarios, quality communication between physicians, patients, and families with realistic discussion of outcomes and maintenance of hope and dignity can facilitate decisions about the use of intensive care for patients with AIDS.