Background Polyp assessment is multimodal and is vital prior to endoscopic mucosal resection. The size, morphology, site and access (SMSA) score has been validated in specialist endoscopic institutions. this study investigated the ability of this score to predict incomplete endoscopic resection of large colorectal polyps in a district general hospital Methods Consecutive patients undergoing endoscopic mucosal resection of large (≥ 20 mm) colorectal polyps at Worthing Hospital. Clinical, endoscopic and histological data were taken from prospective databases. The primary outcome of the study was to investigate the correlation of the SMSA score with incomplete endoscopic resection. Results Between February 2015 and August 2018, 114 patients underwent colorectal endoscopic mucosal resection. Of these, 67 (59%) were male. The median (interquartile range) age of the study population was 72 years (65–78 years). Some 17 lesions (15%) were pedunculated, 76 (67%) were sessile and 21 were (18%) flat; 84 polyps (77%) were located in the left colon/rectum, with the remainder in the right colon; 51 lesions (45%) were 20–30 mm, 27 (24%) were 30–40 mm and 36 (31%) were greater than 40 mm in diameter. When reclassified into the SMSA score, 9 of the polyps (8%) were level 2, 64 (56%) were level 3 and 41 (36%) were level 4. Incomplete resection was clinically diagnosed in 9/114 (8%). The SMSA score was positively correlated with incomplete endoscopic resection, but not with additional procedure usage, complications or advanced histology. Conclusions Many patients with large polyps can be managed outside of specialist units. This study has validated that the SMSA score was associated with incomplete endoscopic mucosal resection for large polyps in a district general hospital setting.