Over a 12-month period, 56 patients with acute exacerbations of chronic sinusitis were included in this study. The mean age of the patients was 48.6 +/- 10.1 years. The period between the onset of sinus symptoms and inclusion in the study was 10.1 +/- 12.1 years and the exacerbation had lasted 2.4 +/- 4.4 months. Patients were given 500 mg ciprofloxacin twice daily for 9 days. Bacteriological specimens taken at inclusion were positive in 53.6% of cases, 25 Gram-positive and 16 Gram-negative pathogens being isolated. At the end of the treatment, rhinorrhoea, which was the main criterion for evaluation of the efficacy of treatment, had disappeared in 46/54 (85%) patients who were examined. Of the 30 patients whose sinusitis was confirmed by bacteriological test, the bacteria were eradicated in 90% of cases. At the end of a 4-week follow-up period after the end of treatment, the clinical success rate was 74.5%, the partial success rate 21.2% and the failure rate 4.3%. There were no bacteriological recurrences. Ten adverse events were observed in seven patients and in four (7%) of these treatment had to be withdrawn. This study showed ciprofloxacin to be an effective and well tolerated treatment for exacerbations of chronic sinusitis treated in non-hospital practice.