Quality-of-life considerations in physicians' decisions on life-sustaining therapy were explored using a patient management problem (PMP) depicting acute respiratory failure in an elderly man with chronic pulmonary disease; 205 internal medicine and family medicine physicians were interviewed. The physicians' perceptions of the patient's quality of life demonstrated marked variability. Physicians considered the patient's quality of life more often to support decisions to withhold therapy than to support decisions to use mechanical ventilation (p less than 0.01). Consideration of quality of life was associated significantly with several PMP components: interpretation of the patient's prior medical experience, management of supplementary case information, attitudes about medical responsibilities/patient rights, and estimates of the patient's survival time. The authors conclude that consideration of quality of life in making life-and-death treatment decisions may involve judgments about the value of life, and that responsible consideration requires guidelines grounded in ethical principles.