We investigated the impact of a novel antibiotic prescription system on antibiotic use. After a two-month baseline monitoring period, an antibiotic prescription form was introduced on surgical and medical wards, which obliged physicians to categorize antibiotic use as prophylactic, empirical (culture results unavailable), or therapeutic. Depending on the category, administration of antibiotics was automatically discontinued after two days (prophylactic), three days (empirical), or seven days (therapeutic) unless the physician renewed the order or specified an alternate duration of administration. In the subsequent two-month intervention period, 233 (60%) of 390 surgical patients received prophylactic antibiotics compared with 281 (68%) of 413 in the baseline period. Mean duration of prophylaxis was reduced from 4.9 +/- 2.4 days to 2.9 +/- 1.6 days. In the intervention period, 11% of patients received their first prophylactic dose postoperatively, compared with a 30% baseline rate. The percentage of urology patients receiving appropriate therapy for urinary tract infection increased from 38% to 89%. No significant changes in antibiotic use were noted on the medical service. This antibiotic prescription system may have a substantial impact on antibiotic use.