OBJECTIVES: Antimicrobial resistance to ciprofloxacin is increasing. The objective of this study was to reduce the number of inappropriate prescriptions and to improve the quality of ciprofloxacin prescriptions by means of educational intervention. METHODS: In a teaching hospital five units of the Departments of Internal Medicine, Gastro-Enterology, Surgery, Urology and Pulmonary Diseases, selected because of a high rate of ciprofloxacin prescription, participated in a prospective intervention study. The quantity and the quality of prescriptions were reviewed before and after educational intervention and during follow-up. The quality of each ciprofloxacin prescription was independently evaluated by two medical microbiologists. During the intervention period, a medical microbiologist discussed the appropriateness of prescribing ciprofloxacin with prescribing clinicians, and educational presentations were given to clinicians of participating units. Regression analysis was used to analyse trends in time-series data. RESULTS: The number of ciprofloxacin prescriptions decreased from 81 prescriptions/1000 admissions before intervention to 32 prescriptions/1000 admissions after intervention, a significant reduction of 60.5%. Appropriate prescriptions significantly increased. Significantly fewer inappropriate prescriptions were prescribed after intervention and/or during follow-up. At this time, 23 ciprofloxacin prescriptions/1000 admissions were prescribed, a total reduction of 71.3% compared with baseline. CONCLUSIONS: In a hospital with relatively low baseline ciprofloxacin consumption, intervention by direct consultation of a medical microbiologist and educational presentations led to 3-4-fold sustained reduction in the use of ciprofloxacin and significant improvement in quality of ciprofloxacin prescriptions. Close collaboration between clinicians and medical microbiologists can provide a major contribution to the prudent hospital use of antimicrobial agents.