Clinical trials can be considered health interventions as their primary aim is to impact on the health of a population. Given that resources are scarce for both health care and health related research, trials could be designed such that they can be demonstrated to be cost-effective, i.e., the costs of conducting the trial are justified given the forecasted long-term benefits. We demonstrate how a model can be used to predict the cost-effectiveness of undertaking a clinical trial comparing alternative regimens of colorectal cancer follow-up. The model forecasts costs and survival under two scenarios, with and without conducting a clinical trial, with the outcome assessed in terms of years to payback for the clinical trial. The methodology shown can be used both to provide information on appropriate trial design and/or in prioritizing between potential trials.