BACKGROUND: Close contact casting (CCC) may offer an alternative to open reduction and internal fixation (ORIF) surgery for unstable ankle fractures in older adults. OBJECTIVES: We aimed to (1) determine if CCC for unstable ankle fractures in adults aged over 60 years resulted in equivalent clinical outcome compared with ORIF, (2) estimate cost-effectiveness to the NHS and society and (3) explore participant experiences. DESIGN: A pragmatic, multicentre, equivalence randomised controlled trial incorporating health economic evaluation and qualitative study. SETTING: Trauma and orthopaedic departments of 24 NHS hospitals. PARTICIPANTS: Adults aged over 60 years with unstable ankle fracture. Those with serious limb or concomitant disease or substantial cognitive impairment were excluded. INTERVENTIONS: CCC was conducted under anaesthetic in theatre by surgeons who attended training. ORIF was as per local practice. Participants were randomised in 1 : 1 allocation via remote telephone randomisation. Sequence generation was by random block size, with stratification by centre and fracture pattern. MAIN OUTCOME MEASURES: Follow-up was conducted at 6 weeks and, by blinded outcome assessors, at 6 months after randomisation. The primary outcome was the Olerud-Molander Ankle Score (OMAS), a patient-reported assessment of ankle function, at 6 months. Secondary outcomes were quality of life (as measured by the European Quality of Life 5-Dimensions, Short Form questionnaire-12 items), pain, ankle range of motion and mobility (as measured by the timed up and go test), patient satisfaction and radiological measures. In accordance with equivalence trial US Food and Drug Administration guidance, primary analysis was per protocol. RESULTS: We recruited 620 participants, 95 from the pilot and 525 from the multicentre phase, between June 2010 and November 2013. The majority of participants, 579 out of 620 (93%), received the allocated treatment; 52 out of 275 (19%) who received CCC later converted to ORIF because of loss of fracture reduction. CCC resulted in equivalent ankle function compared with ORIF at 6 months {OMAS 64.5 points [standard deviation (SD) 22.4 points] vs. OMAS 66.0 points (SD 21.1 points); mean difference -0.65 points, 95% confidence interval (CI) -3.98 to 2.68 points; standardised effect size -0.04, 95% CI -0.23 to 0.15}. There were no differences in quality of life, ankle motion, pain, mobility and patient satisfaction. Infection and/or wound problems were more common with ORIF [29/298 (10%) vs. 4/275 (1%)], as were additional operating theatre procedures [17/298 (6%) vs. 3/275 (1%)]. Malunion was more common with CCC [38/249 (15%) vs. 8/274 (3%); p < 0.001]. Malleolar non-union was lower in the ORIF group [lateral: 0/274 (0%) vs. 8/248 (3%); p = 0.002; medial: 3/274 (1%) vs. 18/248 (7%); p < 0.001]. During the trial, CCC showed modest mean cost savings [NHS mean difference -£644 (95% CI -£1390 to £76); society mean difference -£683 (95% CI -£1851 to £536)]. Estimates showed some imprecision. Incremental quality-adjusted life-years following CCC were no different from ORIF. Over common willingness-to-pay thresholds, the probability that CCC was cost-effective was very high (> 95% from NHS perspective and 85% from societal perspective). Experiences of treatments were similar; both groups endured the impact of fracture, uncertainty regarding future function and the need for further interventions. LIMITATIONS: Assessors at 6 weeks were necessarily not blinded. The learning-effect analysis was inconclusive because of limited CCC applications per surgeon. CONCLUSIONS: CCC provides a clinically equivalent outcome to ORIF at reduced cost to the NHS and to society at 6 months. FUTURE WORK: Longer-term follow-up of trial participants is under way to address concerns over potential later complications or additional procedures and their potential to impact on ankle function. Further study of the patient factors, radiological fracture patterns and outcomes, treatment responses and prognosis would also contribute to understanding the treatment pathway. TRIAL REGISTRATION: Current Controlled Trials ISRCTN04180738. FUNDING: The National Institute for Health Research Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 20, No. 75. See the NIHR Journals Library website for further project information. This report was developed in association with the National Institute for Health Research Oxford Biomedical Research Unit funding scheme. The pilot phase was funded by the AO Research Foundation.