The role of laparoscopic surgery for the treatment of colorectal cancer is being explored in a multi-centre, randomised clinical trial in the UK, the MRC CLASICC Trial (Conventional versus Laparoscopic-assisted Surgery in Colorectal Cancer). An important end-point of the trial is the cost-effectiveness of laparoscopic surgery compared with that of conventional open surgery. The economic evaluation of this trial has been modelled on that in a similar trial being conducted in the USA in colon cancer. The aim of this paper is to discuss the rationale for modelling the UK trial on the US trial, and to describe the adaptations necessary for the UK trial. The parallel design of the economic evaluation in both trials will provide a unique opportunity to compare the cost implications of incorporating laparoscopic surgery in the UK and the USA, and to determine any cross-cultural differences. The UK trial will also provide information about the cost-effectiveness of laparoscopic surgery in rectal cancer.