BACKGROUND: Catheter-associated urinary tract infection (CAUTI) is a major preventable cause of harm for patients in hospital. We aimed to establish whether short-term routine use of antimicrobial catheters reduced risk of CAUTI compared with standard polytetrafluoroethylene (PTFE) catheterisation. METHODS: In our parallel, three group, multicentre, randomised controlled superiority trial, we enrolled adults (aged =16 years) requiring short-term (=14 days) catheterisation at 24 hospitals in the UK. Participants were randomly allocated 1:1:1 with a remote computer allocation to receive a silver alloy-coated catheter, a nitrofural-impregnated catheter, or a PTFE-coated catheter (control group). Patients undergoing unplanned catheterisation were also included and consent for participation was obtained retrospectively. Participants and trial staff were unmasked to treatment assignment. Data were collected by trial staff and by patient-reported questionnaires for 6 weeks after randomisation. The primary outcome was incidence of symptomatic urinary tract infection for which an antibiotic was prescribed by 6 weeks. We postulated that a 3·3% absolute reduction in CAUTI would represent sufficient benefit to recommend routine use of antimicrobial catheters. This study is registered, number ISRCTN75198618. FINDINGS: 708 (10%) of 7102 randomly allocated participants were not catheterised, did not confirm consent, or withdrew, and were not included in the primary analyses. Compared with 271 (12·6%) of 2144 participants in the control group, 263 (12·5%) of 2097 participants allocated a silver alloy catheter had the primary outcome (difference -0·1% [95% CI -2·4 to 2·2]), as did 228 (10·6%) of 2153 participants allocated a nitrofural catheter (-2·1% [-4·2 to 0·1]). Rates of catheter-related discomfort were higher in the nitrofural group than they were in the other groups. INTERPRETATION: Silver alloy-coated catheters were not effective for reduction of incidence of symptomatic CAUTI. The reduction we noted in CAUTI associated with nitrofural-impregnated catheters was less than that regarded as clinically important. Routine use of antimicrobial-impregnated catheters is not supported by this trial. FUNDING: UK National Institute for Health Research Health Technology Assessment Programme.