Background: The magnitude and time course of effect of an acute exacerbation of chronic bronchitis (AECB) on health status are not known. Data from the GLOBE study, a randomised double blind trial of antibiotic therapy, were used to investigate these effects. Methods: 438 patients with AECB received either gemifloxacin 320 mg once daily for 5 days (214 patients) or clarithromycin 500 mg twice daily for 7 days (224 patients) and were followed up for 26 weeks. St George’s Respiratory Questionnaire (SGRQ) scores were obtained at baseline and after 4, 12, and 26 weeks. Results: At presentation during an exacerbation SGRQ scores were worse (Total score difference 5.4 units, 95% CI 1.9 to 8.8, p=0.002) in patients who had a subsequent exacerbation during follow up. The greatest improvement in SGRQ score occurred within the first 4 weeks (mean 8.9 units, 95% CI 6.5 to 11.5, p<0.0001). Subsequently, scores improved more rapidly in patients with no further exacerbations. At 26 weeks the difference between the two groups was 9.6 units (95% CI 5.7 to 13.4, p<0.0001). In patients with no further exacerbations the SGRQ score improved between 4 and 12 weeks by a further 4.1 units (95% CI 2.2 to 5.9, p<0.0001). Conclusions: A single infective AECB has a sustained effect on health status. The recovery period is long even in patients who have no further exacerbations. A second episode within 6 months limits recovery markedly. Treatments that reduce exacerbation frequency could have a significant impact on health status.