In arthroplastic surgery, scientific evidence is often lacking. Haukeland university hospital in Bergen and the Norwegian arthroplasty register are closely tied, and it is natural for us to critically evaluate the usefulness and evidence of new implants and instrumentation. Computer assisted surgery is well documented in neurosurgery, but there have been a few trials in knee replacement surgery suggesting its usefulness. Some of these trials show a better alignment and positioning of the implants (1,10,12). In addition, retrospective trials have shown that the alignment is predictive of implant survival i.e. good alignment gives a better implant survival. (7,8,9) Indirectly that may indicate computer navigation is superior in regard to implant survival. Further one might assume that a better alignment gives a better functional outcome, and this new surgical technique may be less invasive, thus leading to a faster recovery. These questions still remain unanswered.