Prevalence surveys have been part of the Danish infection control programme since 1974. Nationwide surveys were carried out in 1978, 1979, 1980, 1991 and 1999. The results indicate a net reduction of approximately 25%, mainly due to a reduction of urinary tract infections (UTIs) in medical patients. Results from the nationwide surveys are validated by results of occasional independent surveys performed in regions or single hospitals. The reduction coincides with preventive programmes focused on catheter policy and UTI. We conclude that the prevalence survey is an important part of our strategic programme for infection control in hospitals.