Background: Several modalities are available for the diagnosis of rectal cancer, including conventional gold standard rigid endoscopy and recent flexible endoscopy and magnetic resonance imaging (MRI). Each modality affects the management of these patients.Aim: To compare the accuracy of flexible endoscopy and MRI in the measurement of tumor height in patients with rectal cancer. Methods and Results:This study included 174 patients with rectal cancer who underwent flexible endoscopy and MRI for the measurement of tumor height. Data on patient demographics, comorbidities, treatment, and histopathology were identified and collected. We evaluate intraclass correlation coefficient (ICC) and Bland-Altman plot to test the agreement between the measurements. ICC were excellent with an ICC of 89% (95%CI 48%-99%). The mean ± standard deviation of the distance from the anal verge to the distal part of the tumor was 7.73 ± .47 for flexible endoscopy and 6.21 ± 0.39 for MRI, with mean difference of 1.52 (p < .001). The accordance between the two modalities was not affected by sex, age, body mass index, histopathology, or metastasis. Conclusion:Excellent agreement between flexible endoscopy and MRI was noted, and no factor was found to affect such concordance.