ABSTRACT: BACKGROUND: Multiple chemical sensitivity (MCS) is a condition characterized by recurrent, self-reported symptoms from multiple organ systems, attributable to exposure to a wide range of chemically unrelated substances at low levels. The pathophysiology is unknown, and there are currently no evidence-based treatments for MCS. Nevertheless, there is a substantial need for a treatment, because the condition can be severely disabling and can greatly reduce the quality of life (QOL) for those affected.In this study, we aim to assess the effects of a mindfulness-based cognitive therapy (MBCT) program on the impact of MCS on the participants' lives, symptoms, QOL, perceived stress, psychological distress, illness perceptions, and work ability. METHODS: Using a randomized controlled design (RCT), we will compare MBCT with treatment as usual (TAU). The MBCT intervention will include 8 weekly 2.5 hour sessions, and 45 minutes of mindfulness home practice 6 days each week. Participants will be asked to complete questionnaires at baseline, post-treatment, and at 6 and 12 months' follow-up. Based on sample size estimation, 82 participants will be randomized to either the MBCT intervention or to TAU. The primary outcome measure will be the impact of MCS on the participants' lives. The secondary outcome measures are symptoms of psychological distress, perceived stress, illness perceptions, QOL, and work ability. Lastly, we will assess whether any effect of MBCT on the primary effect measure is mediated by level of mindfulness, perceived stress, and rumination. DISCUSSION: This trial will provide important information on the effects of MBCT on MCS.Trials registrationClinical trials identifier NCT01240395.