Background. Optimal bowel preparation is one of the most important factors affecting the quality of colonoscopy. Several patient-related factors are known to influence the quality of bowel cleansing but randomized trials in this area are lacking. We aimed to compare an individualized bowel prep strategy based on patient characteristics to a standard preparation regimen. Material and Methods. We conducted an endoscopist-blinded multicenter randomized control-trial. The Boston Bowel Prep Score (BBPS) was used to assess quality of bowel preparation and a 10 point visual analogue scale to assess patient comfort during bowel prep. Patients were randomised to either the standard regimens of split-dose 4L polyethylene-glycol (group A), split-dose sodium picosulphate/magnesium citrate (group B) or to either of the two depending on their responses to a 3-item questionnaire (individualized preparation, group C). Results. 185 patients were randomized during the study period and 143 patients were included in the final analysis. Patients in the individualized group had a median BBPS of 7 compared to a median of 6 in the standard group (p = 0.7). Also, there was no significant difference in patients’ comfort scores, irrespective of study group or laxative regimen. However, on multivariable analysis, a split-dose 4L polyethylene-glycol was an independent predictor for achieving a BBPS>6 (OR 3.7, 95% CI 1.4-9.8), regardless of patient-related factors. Conclusion. The choice of laxative seems to be more important than patient-related factors in predicting bowel cleansing. Comfort during bowel prep is not influenced by the type of strategy used.