Abstract Risk assessment scales are widely used to measure the risk of pressure ulcers in the clinical area. They have been subject to many validation studies; however these have focused on the predictive ability of the scales. We have conducted several studies that consider the validity of pressure ulcer risk assessment scales. We have reviewed these and revisited the data in some cases to conduct additional tests of validity presented for the first time in this paper. Based on these results, and a review of the literature, we have come to the conclusion that while the scales are probably reliable, and do assess risk: 1. Many of the components of risk assessment scales are not predictive of pressure ulcers 2. There are other variables that are routinely available to clinicians that give additional predictive power 3. The importance of components is not accurately reflected by their range of values 4. Components are correlated and some components may be removed with no loss of predictive power 5. There is no evidence the use of risk assessment scales reduces pressure ulcer incidence The complexity of risk assessment scales does not appear to be warranted. There is evidence that clinical judgment is as effective in assessing risk as risk assessment scales. Reduction in pressure ulcer incidence after implementation of risk assessment tools is likely to be an example of the Hawthorn effect. We believe risk assessment scales are useful research tools, but may not be useful in clinical practice.