BACKGROUND: Individuals with a history of recurrent depression have a high risk of repeated depressive relapse/recurrence. Maintenance antidepressant medication (m-ADM) for at least 2 years is the current recommended treatment, but many individuals are interested in alternatives to m-ADM. Mindfulness-based cognitive therapy (MBCT) has been shown to reduce the risk of relapse/recurrence compared with usual care but has not yet been compared with m-ADM in a definitive trial. OBJECTIVES: To establish whether MBCT with support to taper and/or discontinue antidepressant medication (MBCT-TS) is superior to and more cost-effective than an approach of m-ADM in a primary care setting for patients with a history of recurrent depression followed up over a 2-year period in terms of preventing depressive relapse/recurrence. Secondary aims examined MBCT's acceptability and mechanism of action. DESIGN: Single-blind, parallel, individual randomised controlled trial. SETTING: UK general practices. PARTICIPANTS: Adult patients with a diagnosis of recurrent depression and who were taking m-ADM. INTERVENTIONS: Participants were randomised to MBCT-TS or m-ADM with stratification by centre and symptomatic status. Outcome data were collected blind to treatment allocation and the primary analysis was based on the principle of intention to treat. Process studies using quantitative and qualitative methods examined MBCT's acceptability and mechanism of action. MAIN OUTCOMES MEASURES: The primary outcome measure was time to relapse/recurrence of depression. At each follow-up the following secondary outcomes were recorded: number of depression-free days, residual depressive symptoms, quality of life, health-related quality of life and psychiatric and medical comorbidities. RESULTS: In total, 212 patients were randomised to MBCT-TS and 212 to m-ADM. The primary analysis did not find any evidence that MBCT-TS was superior to m-ADM in terms of the primary outcome of time to depressive relapse/recurrence over 24 months [hazard ratio (HR) 0.89, 95% confidence interval (CI) 0.67 to 1.18] or for any of the secondary outcomes. Cost-effectiveness analysis did not support the hypothesis that MBCT-TS is more cost-effective than m-ADM in terms of either relapse/recurrence or quality-adjusted life-years. In planned subgroup analyses, a significant interaction was found between treatment group and reported childhood abuse (HR 1.89, 95% CI 1.06 to 3.38), with delayed time to relapse/recurrence for MBCT-TS participants with a more abusive childhood compared with those with a less abusive history. Although changes in mindfulness were specific to MBCT (and not m-ADM), they did not predict outcome in terms of relapse/recurrence at 24 months. In terms of acceptability, the qualitative analyses suggest that many people have views about (dis)/continuing their ADM, which can serve as a facilitator or a barrier to taking part in a trial that requires either continuation for 2 years or discontinuation. CONCLUSIONS: There is no support for the hypothesis that MBCT-TS is superior to m-ADM in preventing depressive relapse/recurrence among individuals at risk for depressive relapse/recurrence. Both treatments appear to confer protection against relapse/recurrence. There is an indication that MBCT may be most indicated for individuals at greatest risk of relapse/recurrence. It is important to characterise those most at risk and carefully establish if and why MBCT may be most indicated for this group. TRIAL REGISTRATION: Current Controlled Trials ISRCTN26666654. FUNDING: This project was funded by the NIHR Health Technology Assessment programme and the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care South West Peninsula and will be published in full in Health Technology Assessment; Vol. 19, No. 73. See the NIHR Journals Library website for further project information.