One hundred children scheduled for colonoscopy in southern Sweden will be randomized into either patient group 1 (for preparation with polyethylene glycol) or patient group 2 (for preparation with sodium picosulphate). For the random sampling, data-driven selection will be implemented. A CONSORT Flowchart (2012) will be encompassed by the study. To assess the cleanliness of the intestinal tract (and volume of fluid in the intestine), the Ottawa Scale will be used (Rostom & Jolicoeur, 2009). All colonoscopy examinations will be performed by the same paediatric gastroenterologist, to whom no information about which preparation method was used by each child will be disclosed. Furthermore, the gastroenterologist will, meet with the children first after the investigation has been completed. All information regarding the investigation will be given to the patient by the admitting physician. During the colonoscopy the gastroenterologist will evaluate the intestinal cleanliness and submit the reports in sealed coded envelopes to the nurse in charge of the patient.