BACKGROUND: IBD is considered a relative contraindication to the use of radiation therapy (RT) due to risks of disease exacerbation and GI toxicity. Currently, there are limited available data on how well patients with IBD tolerate RT. METHODS: An electronic search was conducted on PubMed, Cochrane, Embase, and Medline. Eligible studies consisted of all peer-reviewed articles reporting outcomes of RT use in the treatment of abdominopelvic neoplasms in IBD patients. Evidence on RT outcomes is evaluated, namely GI toxicity and IBD activity. RESULTS: A total of 21 articles with 1,226 patients were identified and included. Patients were most commonly treated for prostate cancer (62%). Modes of RT included EBRT (57%), brachytherapy (33%), and stereotactic RT (9%). IBD flares within 6 months of RT ranged between 3.5% and 15%. Risk factors for flares were rectal IBD (p = 0.012) and the concomitant use of chemotherapy and RT (p = 0.02). Common low-grade GI toxicities (grade I-II) were diarrhea (32%) and proctitis (27%). Rectal bleeding ranged from 5 to 23%. Acute grade III-IV GI toxicities ranged between 5 and 23%, while late grade III-IV GI toxicities ranged between 5 and 15%. Patients with IBD receiving RT had significantly higher rates of wound dehiscence and SBO compared to patients without IBD. CONCLUSION: RT in IBD patients can cause acute high-grade toxicity (up to 23%) and late toxicity (up to 15%). Individualized RT decisions considering IBD location and activity are essential. Prospective studies are needed to investigate flares, toxicities, and optimize RT subtypes, doses, and techniques for this population.