The Life Domain Satisfaction Measures and Semantic Differential Scale of General Affect are instruments designed by Campbell to measure perceived well-being. They were used to survey 82 ventilator-assisted individuals with Duchenne muscular dystrophy (DMD) and 273 physically intact health care professionals. A third instrument was devised to study the relative undesirability of dependence on mechanical ventilation. Ten of 80 responding patients (12.5%) expressed dissatisfaction with their lives in general. This compares with 9% of the surveyed health care professionals and 7% of the general population studied by Campbell. The health care professionals significantly underestimated the patients' scores in the life satisfaction and general affect instruments and significantly overestimated the patients' assessment of the relative hardship associated with ventilator dependence. We conclude that the vast majority of severely disabled chronic ventilator-assisted individuals with DMD have a positive affect and are satisfied with life despite the physical dependence which precludes many of the activities most commonly associated with perceived quality of life for physically intact individuals. Health care professionals should not use their judgment of the patient's quality of life to justify withholding life-sustaining therapy.