A review of the records of 17 patients with stage V (fibrotic stage) allergic bronchopulmonary aspergillosis observed since initial diagnosis (mean observation period, 4.9 years) demonstrated that, of the 11 surviving patients, four have very severe respiratory impairment. The other seven patients have mild or moderate functional impairment, but most of these have not shown clinical deterioration during the observation period. The occurrence of new roentgenographic infiltrates after the time of diagnosis was observed in only one patient in this series. Serum IgE and IgG levels against Aspergillus fumigatus, when compared with those of a control pool of serum samples from asthmatic patients with immediate cutaneous reactivity to Aspergillus, were the most useful immunologic studies diagnostically. Lung biopsy specimens obtained in five patients were of relatively little diagnostic value. All patients have required long-term prednisone therapy for control of asthma. Those patients whose forced expiratory volume in 1 s (FEV1) remained less than or equal to 0.8 L after initial corticosteroid treatment demonstrated a poor prognosis. When only moderate lung damage has occurred at the time of diagnosis, a stable subsequent course may be expected even in patients with stage V disease.