Long-term survival data are presented for 200 patients with chronic airway obstruction of uncertain etiology who were enrolled in a prospective study approximately 14 years ago. Early death rates were closely related to the initial level of ventilatory impairment. Subjects with relatively mild impairment on entry to the study had a favorable prognosis for the first 5 to 7 years of follow-up but then began to show a higher death rate; there are few long-term survivors in the total series.