We evaluated the accuracy of the use of an antibiotic prescription-based (APB) case-finding program to identify healthcare-associated infections (HAIs) by carrying out a retrospective review of all patient records in the adult ICU in a tertiary care Finnish teaching hospital in one year. The concordance between the program and our retrospective review was 91.7%. Of all prescribed antibiotics, 12.4% were for HAIs. The case-finding program produces large amounts of data, only a small fraction of which is useful for estimating the incidence of HAIs. Case-finding needs automatic data processing using multiple sources of information.