A review is given of the historical and current concepts of adjuvant chemo- and radiotherapy of colorectal cancer. Early studies analyzing the use of single drug regimens were followed by a second study generation investigating adjuvant chemotherapeutic combinations. 5-FU proved to be the most efficient single drug investigated and 5-FU/MeCCNU/vincristin the most efficient chemotherapeutic combination, but no significant improvement in 5-year survival rates was achieved. Clear progress was noted with the introduction of levamisol (LEV) for modulation of 5-FU. A 33% improval in the 5-year survival rate in patients with stage III colon carcinoma was documented. It was therefore recommended (NIH consensus conference 1990) that all patients with stage III colon carcinoma be treated with this regimen unless admitted to other trials of adjuvant therapy. Preoperative radiotherapy with a dosage of 35-45 Gy can lead to downstaging of rectal cancer. Nevertheless, significant improvement in patient survival has not been proved convincingly using either isolated pre- or postoperative adjuvant radiotherapy. However, combined radiochemotherapy has been shown to improve both patient survival and local tumor control compared to surgical resection alone. It is therefore recommended that all stage II and III rectal cancer patients be treated with adjuvant combined radiochemotherapy. 5-FU/MeCCNU is currently expected to be the most efficient chemotherapy in combination with radiotherapy. Early data point out that MeCCNU could possibly be omitted. Intraoperative radiotherapy (IORT) allows further dosage escalation in order to improve local tumor control without affecting radiosensitive structures. Available data are still sparse and mostly based on the treatment of advanced carcinoma. A general validation of IORT is not yet possible, but current data are promising.