BACKGROUND AND OBJECTIVES: In 1990, the Commission for Anti-infectious Agents of the Swiss Society for Infectious Diseases decided to monitor trends in hospital consumption of antibiotics to understand better and rationalize their use. This article describes and analyzes the evolution in the use of aminoglycosides in Swiss university hospitals. METHODS: Annual consumption figures for four aminoglycosides were provided by pharmacists of participating hospitals for the period 1990-1993. RESULTS: Between 1990 and 1993, the overall consumption of oral and intravenous (i.v.) antibiotics increased by 22% and 38% respectively. On average, 38% of hospitalized patients were receiving antibiotics in 1993 (0.38 daily defined doses [DDD]/day). Aminoglycosides represented 11.3% of all i.v. antibiotics in 1990. There were wide differences between hospitals (range: 7.9 to 36.3% DDD per 1000 days). The four-year trend showed relative stability of use in four hospitals and wide variations in two. Overall, gentamycin remains the most commonly used aminoglycoside while amikacin is less used and retains its role of second line drug. CONCLUSION: The analysis of hospital consumption of aminoglycosides in Swiss university hospitals shows that the trend in use is not identical in all hospitals and that there are wide differences between hospitals (some hospitals use five times more than others). Although the reasons for these differences remain unclear, this monitoring system provides the data needed to formulate and evaluate recommendations designed to rationalize the use of aminoglycosides.