We investigated decisions to withhold or withdraw life support from patients in the medical-surgical intensive care units at the Moffitt-Long Hospital of the University of California and San Francisco General Hospital, from July 1987 through June 1988. Among 1719 patients admitted to the two intensive care units, life support was withheld from 22 (1 percent) and withdrawn from 93 (5 percent). The reason for limiting care was poor prognosis. Of these 115 patients (18 of whom were considered brain-dead), 89 died in the intensive care unit (accounting for 45 percent of all deaths there), and all but 1 of the remaining patients died after transfer from the intensive care unit. Thirteen (11 percent) had earlier expressed the wish that their terminal care be limited, but this affected care in only four cases. Only 5 of the 115 patients made the actual decision to limit care; the others were incompetent at the time. Of the latter, 102 had families who participated in the decision; family members of the other 8 incompetent patients could not be found, and the decisions were made by physicians. Only 10 families initially disagreed with the recommendations to limit care, and they later agreed. The median duration of intensive care among the patients from whom life support was withheld or withdrawn was eight days at Moffitt-Long Hospital and four days at San Francisco General, as compared with medians of three and one days, respectively, for other patients who died in the intensive care units. We conclude that although life-sustaining care is withheld or withdrawn relatively infrequently from patients in the intensive care unit, such decisions precipitate about half of all deaths in the intensive care units of the hospitals we studied. In most of these cases the patients are incompetent, but physicians and families usually agree to limit care.