Background: Colorectal cancer (CRC) is currently one of the most frequently diagnosed cancers. Our aim was to evaluate transparency and selective reporting in interventional trials studying CRC. Methods: First, we assessed indicators of transparency with completeness of reporting, according to the CONSORT statement, and data sharing. We evaluated a selection of reporting items for a sample of randomized controlled trials (RCTs) studying CRC with published full-text articles between 2021-03-22 and 2018-03-22. Selected items were issued from the previously published CONSORT based peer-review tool (COBPeer tool). Then, we evaluated selective reporting through retrospective registration and primary outcome(s) switching between registration and publication. Finally, we determined if primary outcome(s) switching favored significant outcomes. Results: We evaluated 101 RCTs with published full-text articles between 2021-03-22 and 2018-03-22. Five trials (5%) reported all selected CONSORT items completely. Seventy-four (73%), 53 (52%) and 13 (13%) trials reported the primary outcome(s), the allocation concealment process and harms completely. Twenty-five (25%) trials were willing to share data. In our sample, 49 (49%) trials were retrospectively registered and 23 (23%) trials had primary outcome(s) switching. The influence of primary outcome(s) switching could be evaluated in 16 (16/23 = 70%) trials, with 6 (6/16 = 38%) trials showing a discrepancy that favored statistically significant results. Conclusions: Our results highlight a lack of transparency as well as frequent selective reporting in interventional trials studying CRC.