The occurrence of pressure ulcers is widely accepted as an indicator of the quality of health care provided, and quality targets and financial penalties are linked to data on pressure ulcer occurrence. Therefore it is very important that the counting of pressure ulcers is carried out in a thorough and precise way, but frequently this is not the case. The purpose of this article is to describe current limitations in the measurement of pressure ulcer prevalence, and to outline a thorough and systematic methodology for collecting pressure ulcer prevalence data.