Physicians increasingly are being called upon to make difficult decisions about intensive care for patients with the acquired immunodeficiency syndrome (AIDS). AIDS patients who require intensive care have a poor prognosis; the in-hospital mortality rate of those receiving mechanical ventilation for P carinii pneumonia is 86-100 percent in most studies. However, in the past year, two studies documenting improved outcome have been published. Physicians should understand these outcome data and use well-established ethical principles to allow informed competent patients with AIDS to express their preferences regarding intensive care. Patients should be encouraged to provide advanced directives regarding life-sustaining treatments or to designate surrogate decision-makers to be consulted should they lose mental competence. The health care system should provide alternatives to the ICU for compassionate terminal care. However, arbitrary policies denying intensive care to AIDS patients for whom it is medically indicated and desired are not warranted.