In a multicenter, randomized controlled trial of 665 hospitalized adults undergoing elective colonoscopy, a split-dose 1-L polyethylene glycol (PEG)-ascorbate regimen achieved similar rates of adequate bowel cleansing as 2-L PEG-ascorbate and 4-L PEG (82% vs 78% vs 79%), but higher rates of high-quality cleansing, including in the right colon. Tolerability and adherence were high across groups, with the greatest willingness to repeat seen in the 1-L group despite more frequent vomiting and thirst.