Millions of people have difficulty in emptying their urinary bladder resulting in urinary retention or post void residue (PVR). This retention or residue is due to lower urinary tract dysfunction, in which the cause is commonly unknown (idiopathic) or caused by well-known diseases like spinal cord injury (SCI) or multiple sclerosis (MS). To empty the bladder, the treatment of choice is clean intermittent self-catheterization (CIC). Virtually all patients on CIC in the Netherlands utilize single use (=disposable) catheters. The possible advantages of reusable catheters include more patient choice, cost saving, reducing fear of running out of catheters, and environmental advantages. The possible disadvantages of reusable catheters are increased risk of UTIs, effectiveness of cleaning method, damage to the urethra and increased patient burden. The main objective of the COMPaRE trial is to determine whether the use of reusable catheters in patients on intermittent catheterization for urinary retention is not less safe and not less effective as the use of single use catheters.