We investigated the extent to which bed availability affects decision making in an intensive care unit (ICU). For 1,151 ICU patients, we determined the number of empty ICU beds available at times of admission and discharge and the outcome for those patients. For a randomly chosen group we assessed severity of illness. Patients admitted during times of bed shortage were, on average, more severely ill than those admitted when many beds were unoccupied. Patients discharged under crowded conditions were sicker and had a shorter stay than patients discharged when more beds were available. The relative risk of discharge was inversely related to empty bed availability, illness severity, and age. Bed availability had no effect on rates of death in the ICU, death after discharge, or readmission to the ICU. We conclude that physicians can effectively ration intensive care beds on a regular basis by altering admission and discharge decision making.