A database of the prescriptions of antimicrobial drugs for the treatment of common infectious diseases in dogs at the Finnish Veterinary Teaching Hospital was searched to determine to what extent national guidelines were being followed. Twenty-two per cent of 5918 dogs were treated orally with antimicrobial drugs. The most commonly used drugs were beta-lactams (49 per cent) of which cephalexin and amoxycillin-clavulanate were most widely prescribed. The usage of fluoroquinolones was only 2·8 per cent. The prescription of antimicrobials for pyoderma was contrary to Finnish guidelines, but the use of cephalexin or amoxycillin-clavulanate as first-line drugs instead of macrolides or lincosamides or trimethoprim-sulphonamides was acceptable because of the presence of resistance by canine staphylococci. The drug most commonly used to treat acute urinary tract infections was trimethoprim-sulphonamide, in agreement with the guidelines. Antimicrobial drugs were used excessively after surgical procedures, and for treating acute gastrointestinal disturbances and small wounds and traumas.