OBJECTIVE: To determine whether a short course of antibiotic treatment (up to 5 days) is as effective as the conventional longer treatment in acute exacerbations of chronic bronchitis and COPD. METHODS: MEDLINE, EMBASE and the Cochrane central register of controlled trials were searched to July 2006. Eligible were double-blind randomized clinical trials including adult patients >/= 18 years of age with clinical diagnosis of exacerbation of COPD or chronic bronchitis, no antimicrobial therapy at the time of diagnosis and random assignment to antibiotic treatment up to 5 days versus longer than 5 days. Primary outcome measure was clinical cure at early follow-up, on intention to treat basis. RESULTS: 21 studies with a total of 10698 patients were included. The average quality of the studies was high: the mean Jadad score was 3.9 (SD 0.9). At early follow-up (<25 days) the summary odds ratio (OR) for clinical cure with short treatment versus conventional treatment was 0.99 (95% CI 0.90 to 1.08). At late follow-up the summary OR was 1.0 (95% CI 0.91 to 1.10) and the summary OR for bacteriological cure was 1.05 (95% CI 0.87 to 1.26). Similar summary ORs were observed for early cure in trials with the same antibiotic in both arms and in studies grouped by the antibiotic class used in the short-course arm. CONCLUSIONS: A short course of antibiotic treatment is as effective as the traditional longer treatment in patients with mild to moderate exacerbations of chronic bronchitis and COPD.