This is the database for final analysis of the PRECOL clinical trial, whose abstract follows Background. Adequate bowel preparation before colonoscopy is crucial. Unfortunately, up to 25% of all colonoscopies have inadequate bowel cleansing. From a patient perspective, bowel preparation is a main obstacle for colonoscopy. Several low-volume bowel preparations have been formulated to provide more tolerable purgative solutions without loss of efficacy. Methods: In this phase 4, randomized, multicenter, two-arm trial, adult outpatients undergoing colonoscopy received either Sodium Picosulphate plus Magnesium Citrate (SPMC) or Polyethylene Glycol plus Ascorbic Acid (PEG-ASC) for bowel preparation. The primary aims were to test quality of bowel cleansing (primary endpoint, scored according the Boston Bowel Preparation Scale) and patient’s acceptance (measured with 6 visual analogue scales). The study was open as for treatment assignment, and blinded for primary endpoint assessment that was done independently on videotaped colonoscopies by 2 endoscopists not aware of study arm. A sample size of 525 patients was calculated to recognize a difference of 10% in the proportion of successes between the arms with a two-sided alpha error of 0·05 and 90% statistical power. Findings: overall 550 subjects (279 assigned to PEG-ASC and 271 assigned to SPMC) represented the analysis population. There was no statistically significant difference in the success rate according to BBPS: 94·4% with PEG-ASC and 95·7% with SPMC (P=0·49). Acceptance and willing to repeat were significantly better for SPMC with all the scales. Compliance was less than full in 6·6% and 9·9% of cases with PEG-ASC and SPMC, respectively (P=0·17). Nausea and meteorism were significantly more bothersome with PEG-ASC than SPMC. There were no serious adverse events in either group. Interpretation. SPMC and PEG-ASC are not different in terms of efficacy, but SPMC is better tolerated than PEG-ASC. SPMC could be used as alternative to low-volume PEG based purgative solutions for bowel preparation. Funding. This research had no financial support. ClinicalTrials.gov NCT01649674; EudraCT 2011—000587—10.