Background: We evaluated outcomes of intraoperative radiotherapy delivered with focal high-dose-rate (HDR) brachytherapy [intraoperative radiotherapy (IORT)] in the management of locally recurrent (LR) and locally advanced (LA) primary T4 colorectal carcinoma (CRC). LR CRC or LA primary disease is a clinical challenge due to the difficulty in obtaining negative margins after radical surgery and the high risk of subsequent recurrence. Few data exist on long-term outcomes of patients treated with surgery and HDR-IORT for LR or LA primary CRC. Methods: Three hundred CRC patients underwent HDR-IORT to the pelvis with gross surgical resection during November 1992–December 2007. Median follow-up for surviving patients was 53 (range 5–216) months. Eighty-eight patients (29 %) were treated for LA primary and 212 (71 %) LR disease. HDR-IORT was delivered using an iridium-192 remote afterloader and a Harrison–Anderson–Mick applicator. Median IORT dose was 1,500 (range 1,000–2,000) cGy. Results: Five-year overall survival probability was 49 %. Positive margin status was associated with inferior overall survival and disease-free survival. Competing-risks analysis for time to local failure and distant metastases identified a 5-year cumulative incidence of local failure and distant metastases of 33 and 47 %, respectively. Five-year cumulative incidence of local failure was 22 % for the LA group and 38 % in the LR group. Five-year probability of disease-free survival was 48 and 31 % for LA and LR patients, respectively, and 5-year probability of overall survival was 56 and 45 % for LA and LR patients, respectively. Conclusions: HDR-IORT combined with resection results in encouraging local control rates with acceptable toxicity for patients with locally aggressive CRC.