We followed the course of 36 consecutive patients hospitalized with chronic obstructive pulmonary disease and acute respiratory failure due to exacerbation of chronic bronchitis in order to clarify the prognosis in this common group of patients. All of the patients had spirometric evidence of severe, poorly reversible airflow limitation and all had a similar cause of acute respiratory failure. In addition, all received similar treatment during hospitalization and follow-up. Patients wtih asthma and pneumonia were excluded by clinical, spirometric, and roentgenographic criteria. Hospital survival was 94 percent, and only one patient required intubation. Two-year survival was 72 percent, and none of the patients died during a readmission for acute respiratory failure. This prognosis is much better than commonly recognized and compares favorably to that of stable outpatients with similar degrees of airflow limitation. An episode of acute respiratory failure, triggered by an exacerbation of chronic bronchitis, does not necessarily alter the prognosis of patients with COPD.