Background: Pelvic radiotherapy with concurrent 5-fluorouracil based chemotherapy (chemoradiation) is a component of standard therapy for patients with T3/T4 or node-positive rectal cancer. Chemoradiation can be associated with significant acute gastrointestinal toxicity. This study sought to retrospectively compare patient and clinician reports of acute symptoms experienced by rectal cancer patients receiving chemoradiation. Methods: The charts of 199 rectal cancer patients who received chemoradiation from 11/06 to 2/11 were reviewed. Clinicians assessed toxicity weekly using Common Terminology for Clinical Adverse Event (CTCAE) version 3.0. Patient-reported outcomes (PROs) were collected weekly, in clinic, beginning 9/09 using the 7-item Bowel Problems Scale. 197 patients had at least one clinician assessment or PRO and were eligible for this study. Patient and clinician assessments were compared among a subgroup of 65 patients (paired group) who had at least one patient and clinician assessment on the same date using descriptive statistics. Agreement between patient and clinician assessments was evaluated by Cohen’s kappa coefficient. Results: Characteristics were well-balanced between all rectal patients and the paired group, with the exception of the use of intensity modulated radiotherapy (IMRT). IMRT has been used increasingly over time, and IMRT was therefore used in a larger proportion of the paired group versus all patients (77% vs. 51%, respectively). Diarrhea and proctitis were reported more often by patients than clinicians throughout treatment. Uncorrected agreement for diarrhea and proctitis was 82% and 72%, respectively. Corrected for chance, Cohen’s kappa was .64 for diarrhea, indicating moderate agreement, and .22 for proctitis, indicating only slight agreement. Conclusions: Our findings suggest a discrepancy between clinician and patient symptom reports. Further study is warranted to discern potential benefits of including PROs in prospective studies, and to find whether PROs can help clinicians set patient expectations, and/or enhance communication for optimal symptom management.