According to the results of several studies intraoperative radiotherapy seems to influence local control for primary rectal cancer in UICC-Stage II / III positively, though recommendations in therapy cannot be given as studies of high evidence level do not exist. As IORT is rarely available and makes patient recruitment difficult, prospective randomised trials have not been carried out yet. This emphasizes the importance of non-randomised trials for an evaluation of IORT. A comparison of 21 patients with locally advanced rectal cancer who had been treated with intraoperative radiation therapy and 21 similar cases without an application of IORT could not show any significant improvements in prognosis (recurrences, metastases and disease-specific survival). Nevertheless the employment of intraoperative radiation showed a trend in improvement of local control. This hast been shown by several other studies before. Thus the application of IORT in patients with locally advanced rectal cancer is considered a useful part in multimodal treatment and should further be evaluated in specialized centres. In case-control studies 1:1-matching leads to a good comparability of groups and renders conclusions of high internal validity possible. To gain a sufficient power, this type of trials should however primarily be carried out by centres with a high number of cases