Pulmonary eosinophilic granuloma is an uncommon disease of unknown origin with characteristic pathologic features. Reports of long-term follow-up in this disorder are rare in the literature. We report the course of a patient followed at our institution from diagnostic lung biopsy through autopsy over 25 yrs. His case represents the longest follow-up reported to our knowledge and demonstrates that (1) despite apparent clinical stability, ongoing injury may result in gradually progressive respiratory impairment and death after many years, and (2) despite changes diagnostic of pulmonary eosinophilic granuloma at lung biopsy early in the course, autopsy may reveal only end-stage fibrosis with honeycombing.