OBJECTIVES: Health technology assessments (HTAs) have the potential to influence the diffusion of medical devices into health care systems. This study investigates the impact the National Institute for Health and Clinical Excellence’s (NICE) technology appraisals have on the diffusion of implantable devices in the United Kingdom (UK). METHODS: The analysis focused on the impact of NICE guidance on volume sold of three medical devices: drug eluting stents (DES), implantable cardioverter defibrillators (ICD), and spinal cord stimulators (SCS). UK sales data (2005-2010) for each device were collected from Eucomed and other industry sources. Diffusion patterns before and after publication of NICE guidance were analyzed from an aggregated market-level perspective. A linear regression model was fit to the time series data to illustrate the relationship between the NICE decision and volume.   RESULTS: The results from the statistical analysis show that NICE guidance has different effects on diffusion across products.  NICE guidance had a step increase impact in adoption of DES and SCS (p=0.026 and p=0.00, respectively).The model suggests that the NICE review did not predict the diffusion of ICDs. Descriptive analysis demonstrated that for SCS and ICDS the NICE decision had a positive effect and no impact on DES diffusion on volume over time. Overall the units sold were positively and significantly correlated with time post-NICE guidance. CONCLUSIONS: The study indicates that NICE guidance influences the adoption of medical devices. Positive recommendations were associated with an increase in units sold despite a decrease in units sold experienced before the final recommendation. Additionally, the analysis suggests that there may be a lag between a positive NICE decision and adoption of guidance recommendations in practice.  Lastly, there were no consistent trends on NICE’s effect on the rate of diffusion. More research is needed to clearly understand the dynamics of HTAs on technology adoption.