The National Institute of Excellence (NICE) released its first guidance in 2000 on clinical procedures and technologies in England and Wales. Using hospital activity data, we looked at the effect of NICE guidance on wisdom tooth extraction and primary total hip replacement in the UK National Health Service. We selected hospitals that submitted their activity continuously between 1997 and 2002. Analysis of wisdom tooth extraction showed that NICE guidance was not the primary reason for the downward trend in extractions (p=0.8287); this trend was more likely to be attributable to previous guidance. For total hip replacement there was no significant change in behaviour away from use of non-cemented hip prostheses. Therefore, NICE guidance has had little effect on behaviour for these two procedures.