The classification of pressure ulcers constitutes an essential part of patient assessment and forms a baseline on which to monitor patients' progress and measure the outcomes of care. Four classification systems - Torrance, National Pressure Ulcer Advisory Panel, European Pressure Ulcer Advisory Panel, and Stirling - are discussed. Many classification systems have been adopted by trusts despite insufficient research in their use in clinical practice. Regardless of which classification system is implemented, nurses need to be familiar with the one they are using and how to stage accurately a pressure ulcer. This can only be attained through regular education.