Abstract Background Polyethylene glycol (PEG)-based bowel preparations are effective cleansers but many require high-volume intake. This phase 3, randomized, blinded, multicenter, parallel-group, central reader-assessed study assessed the 1 L PEG NER1006 bowel preparation vs. standard 2 L PEG with ascorbate (2LPEG). Methods Patients undergoing colonoscopy were randomized (1:1:1) to receive NER1006, as an evening/morning (N2D) or morning-only (N1D) regimen, or evening/morning 2LPEG. Cleansing was assessed using the Harefield Cleansing Scale (HCS) and the Boston Bowel Preparation Scale (BBPS). Primary end points were overall bowel cleansing success and high-quality cleansing in the right colon. Modified full analysis set (mFAS) and per protocol (PP) analyses were performed. Mean cleansing scores were analyzed post hoc. Results Of 849 randomized patients, efficacy was analyzed in the following patient numbers (mFAS/PP): total n = 822/670; N2D n = 275/220; N1D n = 275/218; 2LPEG n = 272/232. mFAS established noninferiority. PP showed superiority for N2D on overall success (97.3 % vs. 92.2 %; P = 0.014), and for N2D and N1D on right colon high-quality cleansing (N2D 32.3 % vs. 15.9 %, P < 0.001; N1D 34.4 % vs. 15.9 %, P < 0.001) vs. 2LPEG. Using HCS, N2D and N1D attained superior segmental high-quality cleansing (P ≤ 0.003 per segment). N2D showed superior mean segmental HCS scores (P ≤ 0.007 per segment). Both N2D and N1D achieved superior mean overall (P < 0.001 and P = 0.006) and right colon BBPS scores (P < 0.001 and P = 0.013). N2D demonstrated superior right colon polyp detection (P = 0.024). Adherence, tolerability, and safety were comparable between treatments. Conclusions NER1006 is the first low-volume preparation to demonstrate superior colon cleansing efficacy vs. standard 2LPEG with ascorbate, with comparable safety and tolerability. European Clinical Trials Database (EudraCT)2014-002185-78TRIAL REGISTRATION: Multicenter, randomized, parallel group, phase 3 trial 2014-002185-78 at https://eudract.ema.europa.eu/