context: colonoscopy is currently the gold standard method to examine the colon, the rectum and the terminal ileum. in order to perform the colonoscopy, it is necessary to clean the bowel and use medications that are generally poorly tolerated by the patients. objective: compare the tolerability, acceptability, safety and efficacy of two solutions used for intestinal preparation for a colonoscopy. methods: one hundred patients matched for sex and age were prospective randomized into two groups. polyethylene glycol group received bisacodyl 10 mg plus 1 l of polyethylene glycol the night before and 1 l on the day of the exam. mannitol group received bisacodyl 20 mg the day before and 1 l of a 10% mannitol solution on the day of the exam. the diet was the same for both groups. tolerability and acceptability were measured using previously validated questionnaires. in terms of safety, variations in vital signs before and after the preparation were recorded, in addition to any complications. the quality of the preparation was graded based on the boston and ottawa scales. results: ninety-six percent (96%) completed the study. as for tolerability, the mannitol preparation group exhibited a significantly higher frequency of nausea, vomiting, abdominal pain, and abdominal distension than polyethylene glycol group (p < 0.05). acceptability was significantly better in polyethylene glycol group. the polyethylene glycol solution has also previously been shown to be safer than mannitol. no difference was observed in the quality of the preparation between the two preparation methods. conclusions: the following conclusions can be made: polyethylene glycol solution had higher tolerability, acceptability, and safety than the mannitol and should be used instead of mannitol. both preparation solutions have similar efficacy.