Background Lower urinary tract symptoms (LUTS) in men may indicate bladder outlet obstruction (BOO) or weakness, known as detrusor underactivity (DU). Severe bothersome LUTS are a common indication for surgery. The diagnostic tests may include urodynamics (UDS) to confirm whether BOO or DU is the cause, potentially reducing the number of people receiving (inappropriate) surgery. Objectives The primary objective was to determine whether a care pathway including UDS is no worse for symptom outcome than one in which it is omitted, at 18 months after randomisation. Rates of surgery was the key secondary outcome. Design This was a pragmatic, multicentre, two-arm (unblinded) randomised controlled trial, incorporating a health economic analysis and qualitative research. Setting Urology departments of 26 NHS hospitals in England. Participants Men (aged ≥ 18 years) seeking further treatment, potentially including surgery, for bothersome LUTS. Exclusion criteria were as follows: unable to pass urine without a catheter, having a relevant neurological disease, currently undergoing treatment for prostate or bladder cancer, previously had prostate surgery, not medically fit for surgery and/or unwilling to be randomised. Interventions Men were randomised to a care pathway based on non-invasive routine tests (control) or routine care plus invasive UDS (intervention arm). Main outcome measures The primary outcome was International Prostate Symptom Score (IPSS) at 18 months after randomisation and the key secondary outcome was rates of surgery. Additional secondary outcomes included adverse events (AEs), quality of life, urinary and sexual symptoms, UDS satisfaction, maximum urinary flow rate and cost-effectiveness. Results A total of 820 men were randomised (UDS, 427; routine care, 393). Sixty-seven men withdrew before 18 months and 11 died (unrelated to trial procedures). UDS was non-inferior to routine care for IPSS 18 months after randomisation, with a confidence interval (CI) within the margin of 1 point (–0.33, 95% CI –1.47 to 0.80). A lower surgery rate in the UDS arm was not found (38% and 36% for UDS and routine care, respectively), with overall rates lower than expected. AEs were similar between the arms at 43–44%. There were more cases of acute urinary retention in the routine care arm. Patient-reported outcomes for LUTS improved in both arms and satisfaction with UDS was high in men who received it. UDS was more expensive than routine care. From a secondary care perspective, UDS cost an additional £216 over an 18-month time horizon. Quality-adjusted life-years (QALYs) were similar, with a QALY difference of 0.006 in favour of UDS over 18 months. It was established that UDS was acceptable to patients, and valued by both patients and clinicians for its perceived additional insight into the cause and probable best treatment of LUTS. Limitations The trial met its predefined recruitment target, but surgery rates were lower than anticipated. Conclusions Inclusion of UDS in the diagnostic tests results in a symptom outcome that is non-inferior to a routine care pathway, but does not affect surgical rates for treating BOO. Results do not support the routine use of UDS in men undergoing investigation of LUTS. Future work Focus should be placed on indications for selective utilisation of UDS in individual cases and long-term outcomes of diagnosis and therapy. Trial registration Current Controlled Trials ISRCTN56164274. Funding This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 24, No. 42. See the NIHR Journals Library website for further project information.