Background: Prevention of peritonitis is important to peritoneal dialysis (PD) patients, since it increases the risk for PD technique failure and mortality. Patients non-compliant with the PD exchange protocol procedures more often experience peritonitis than compliant patients. We therefore assessed the effect of regular testing of the PD knowledge in patients new to PD with the primary aim to reduce time to first peritonitis. Methods: This physician-initiated, open-label, parallel group trial was undertaken at 57 centres in Scandinavia, Estonia, Latvia, the Netherlands, and the UK. Patients new to PD and able to perform PD without assistance were randomly assigned in a 1:1 ratio to a retraining or a control group using computer generated randomisation. The retraining patients underwent regular testing of PD knowledge and skills with focus on infection prophylaxis at 1, 3 and 6 months after PD start, and every 6th month thereafter up to 36 months. If they did not pass the tests, they were retrained. The controls were treated according to routines of their centres. Findings: Of 671 participants, 340 were assigned to the retraining group and 331 to the control group. The follow-up after 12, 24, and 36 months was completed by 57%, 23%, and 9% in the retraining group and 67%, 34% and 13% in the controls. 102 (30%) of participants in the retraining group and 121 (37%) of the controls experienced a first peritonitis episode. Compared with the controls, the retraining group did not have significantly longer time to first peritonitis during the study (HR 0·92 (0·71-1·19); p=0·52] or during the first year of follow-up [(HR 0·87 (0·63-1·21); p=0·41]. Interpretation: In this randomised controlled trial, we were unable to demonstrate that regular, targeted testing and retraining of patients new to PD reduced the risk of first peritonitis. Clinical Trial Number: The trial was registered with CinicalTrials.gov, number NCT01293799. Funding Statement: The Health & Medical Care Committee of The Regional Executive Board, Region West of Sweden (VGFOUREG-78061, 226521, and 383641), Baxter Healthcare Corporation (McGaw Park, IL, USA; Clinical Evidence Council grant #10CECEU1004), Swedish Society of Nephrology, The Swedish Kidney Association, The Society of Kidney Patients in West of Sweden, The John and Brit Wennerstrom Foundation, The Foundation for kidney failure, The Swedish Kidney Foundation, and Norwegian Society of Kidney Patients. Declaration of Interests: SL has received a research grant from Baxter Healthcare Corporation, that partly funded this trial. OH has received speaker´s honoraria from Baxter Healthcare Corporation and Fresenius Medical Care, investigator´s honoraria from Fresenius Medical Care and Otsuka, and personal fee for participation in an advisory board regarding hyperkalaemia from Astra Zeneca. MW has received speaker´s honoraria from Fresenius Medical Care. AP has received speaker´s honoraria from Fresenius Medical Care and Baxter Healthcare Corporation and travel grants from Baxter Medical Corporation and Gambro. Ethics Approval Statement: The study protocol (see appendix) was approved by the ethics committees in all participating countries and was in full compliance with the Helsinki Declaration.