Aim: To weigh the harms and benefits of short-term pre-operative radiotherapy in the treatment of resectable rectal cancer. Methods: The benefits (reduction of local recurrence) and harm (increase of short-term complications) of short-term pre-operative radiotherapy are balanced using a model which classifies patients in one of five outcome combinations; 1-benefit without additional harm, 2-benefit with additional harm, 3-no benefit, no additional harm, 4-no benefit but additional harm, 5-mortality due to combined treatment. The results of four randomised clinical trials (RCT) which study the addition of short-term pre-operative radiotherapy in rectal cancer were classified according to this model. Results: Five to thirteen percent of the patients have benefit without additional harm of pre-operative radiotherapy, while 0-2% have benefit with additional harm; 74-87% has neither benefit nor additional harm and 6-11% have no benefit but additional harm. A small percentage of patients (1-6%) dies post-operatively as a result of the addition of radiotherapy. Conclusion: This model provides a transparent appreciation of the harmful and beneficial effects of any treatment modality investigated by means of a randomised clinical trial. As for short-term pre-operative radiotherapy in resectable rectal cancer is shown, a small percentage of patients benefits from such treatment. Most patients have neither benefit nor additional harm, while a small percentage suffers from additional harm while not receiving any benefit.