The objective of this study was to evaluate antibiotic use in relation to diagnoses and bacteriological findings in a 600-bed Norwegian university hospital. Twelve point-prevalence studies of antibiotic use were conducted between 1996 and 1999. In the point-prevalence studies, 1,096 of 6,588 adult patients (16.6%) used on average 1.25 antibiotics each. Of the patients who received antibiotics, 35% were treated for hospital-acquired infections. Lower respiratory tract and urinary tract infections accounted for more than half of all antibiotic use. Pencillins represented 54% of antibiotic use, cephalosporins 9%, quinolones 6% and antifungal agents 0.7%. The prescribed daily doses for the penicillins were 2-3 times higher than the defined daily doses. Bacteriological samples were obtained from 929 (85%) patients. Compliance with the guidelines was > 90% and was highest when the results of bacteriological samples were positive. Good compliance led to low prevalence of antibiotic use and the use of narrow-spectrum antibiotics.