Introduction: Clinically significant serrated lesions (SL) may contribute to colon cancers (AJG 2012;107:1315-30) through a pathway unrelated to the adenoma-cancer sequence (CGH 2016;14:105659). These often subtle and non-polypoid lesions include sessile serrated adenomas/polyps, traditional serrated adenomas and hyperplastic polyps in the proximal colon, and missed lesions may account for interval cancers in proximal colon. Table 1 shows the impact of various combinations of cap (C), water exchange (WE) and chromoendoscopy with indigo carmine added to water (CE) on detection rate (DR) of various lesions (adenomas, serrated lesions) in proximal colon. We hypothesize that cap-assisted total water with chromoendoscopy (CATWCE) can further improve proximal adenoma detection (ADR) and clinically significant serrated lesions detection rate (SLDR) in screening and surveillance colonoscopy. Methods: Retrospective analysis of performance improvement observations in two consecutive series. Colonoscopy was performed with a transparent cap attached to tip of high definition colonoscope (Olympus PCF-H190L). Examination with CATW was performed with plain water and CATWCE used a 0.002 % indigocarmine solution. Air button was turned off. Water was infused and exchanged to remove debris on scope insertion until cecum was reached. Air pockets were suctioned. Water was used on scope withdrawal to facilitate examination and underwater polypectomy with forceps, cold or hot snares. Water was suctioned at dependent locations and tallied. No air was used for either method. Results: A total of 250 patients (125 per group) were included. Patients demographics (age, BMI) were comparable (Table 2). There were more patients for surveillance in CATW and screening in CATWCE. Total amount of water infused/suctioned were comparable. Cecal intubation time and success rate were comparable but withdrawal time was longer for CATWCE. Compared with CATW, CATWCE has significantly higher proximal < 5 mm ADR (67% vs 60% respectively, p< 0.05), and proximal SLDR (33% vs 17%, respectively, p< 0.05) Conclusion: Limitations: Retrospective analysis of non-randomized consecutive series of Veterans, single operator. Conclusion: Combined cap-assisted total water and chromoendoscopy (CATWCE) significantly improved proximal (< 5 mm) ADR and proximal SLDR in screening and surveillance colonoscopy. The role of CATWCE in colorectal cancer prevention including interval cancers deserves further evaluation in a prospective RCT