The aim of the study presented here was to prospectively audit antibiotic prescriptions given to patients attending L'Archet Hospital in Nice, France, with details of the initial medical examination included in the audit procedure. A total of 122 antibiotic treatments were evaluated, i.e. 31% of all antibiotic therapies initiated in the eight participating departments over the 9-week study period. Forty-two (34%) treatments were found to be unnecessary due to misdiagnosis, and 36 (30%) other treatments were inappropriate. Misdiagnosis, due to the misinterpretation or lack of clinical, microbiological and/or imaging data is thus a major cause of antibiotic misuse. Improvement in the diagnostic process should become part of antibiotic policy.