This paper describes an innovative system called Op3D that delivers high performance visualisation to a hospital operating theatre. This is the first time that a hepato-pancreatic surgeon has been able to benefit from 3D visualisation tools at the sharp end of his clinical practice. Early results are supporting our hypothesis that interactive access to 3D visualisation and reconstruction from the operating theatre improves the prospect of successful resection of hepato-pancreatic tumours (and could easily be exploited in other surgical areas too). The implementation of the system is discussed in detail, including all of the software and hardware components involved. The paper ends with a discussion of the future potential of the system to take advantage of high performance computing, visual area networking, and the Grid.