Objective: The efficacy and acceptability of existing psychological interventions for health anxiety (hypochondriasis) are limited. In the current study, the authors aimed to assess the impact of mindfulness-based cognitive therapy (MBCT) on health anxiety by comparing the impact of MBCT in addition to usual services (unrestricted services) with unrestricted services (US) alone. Method: The 74 participants were randomized to either MBCT in addition to US (n = 36) or US alone (n = 38). Participants were assessed prior to intervention (MBCT or US), immediately following the intervention, and 1 year postintervention. In addition to independent assessments of diagnostic status, standardized self-report measures and assessor ratings of severity and distress associated with the diagnosis of hypochondriasis were used. Results: In the intention-to-treat (ITT) analysis (N = 74), MBCT participants had significantly lower health anxiety than US participants, both immediately following the intervention (Cohen's d = 0.48) and at 1-year follow-up (d = 0.48). The per-protocol (PP) analysis (n = 68) between groups effect size was d = 0.49 at postintervention and d = 0.62 at 1-year follow-up. Mediational analysis showed that change in mindfulness mediated the group changes in health anxiety symptoms. Significantly fewer participants allocated to MBCT than to US met criteria for the diagnosis of hypochondriasis, both immediately following the intervention period (ITT 50.0% vs. 78.9%; PP 47.1% vs. 78.4%) and at 1-year follow-up (ITT 36.1% vs. 76.3%; PP 28.1% vs. 75.0%). Conclusions: MBCT may be a useful addition to usual services for patients with health anxiety. (Contains 2 figures, 3 tables, and 3 footnotes.)