Abstract Aims The Joint Advisory Group on GI Endoscopy (JAG) has set key quality indicators for colonoscopy, which includes an adenoma detection rate of a minimum of 15%. Given the difficulty in reporting adenoma detection rate, JAG have stated that polyp detection rate is accepted as a surrogate measure. Our aim was to assess whether polyp detection rate can be used as a substitute marker for adenoma detection, by examining the histology of samples taken as polyps to determine what proportion are truly adenomas. Methods The pathology department provided a registry of all histological samples taken from the colon or rectum during a one-year period April 2017 to April 2018. These samples were cross-referenced with the endoscopy report to assess which were identified as “polyps” by the performing endoscopist. The pathology report was then reviewed to determine what the histological conclusion was for each “polyp”. Results A total of 1601 colorectal histology samples were reviewed, taken by 32 different endoscopists. 451 of these were identified as polyps by the performing endoscopist. On histological review 153 (33.9%) were not adenomas of the colon or rectum. Common alternative histological diagnoses were hyperplastic polyp, inflammatory polyp and normal tissue. Rarer alternative histological diagnoses were melanosis coli, submucosal leiomyoma and endometriosis of the rectum. Conclusions Polyp detection rate which is used as a surrogate marker for adenoma detection rate is an inaccurate measure of colonoscopy quality.