OBJECTIVE: Multiple chemical sensitivity (MCS) is a medically unexplained condition characterized by symptoms from multiple organ systems following the perception of common odorants. The condition can cause severe functional impairment for afflicted individuals. The aim of this study was to assess the effects of mindfulness-based cognitive therapy (MBCT) for individuals with MCS. METHODS: The intention-to-treat sample (ITT) included 69 individuals who had been randomized to either MBCT or treatment as usual (TAU). The primary outcome measure was the Quick Environmental Exposure and Sensitivity Inventory (QEESI), which measures the following aspects of MCS: impact of MCS on daily life, symptoms, and reactions following chemical exposures. Secondary outcome measures included the Brief Illness Perception Questionnaire (BIPQ) and the anxiety and depression subscales of the symptom checklist 92 (SCL-92). Participants were assessed at baseline and post treatment, and at follow-up periods of 6- and 12-months. RESULTS: We found no effect of MBCT on the primary outcome, nor did we find an effect on levels of depression or anxiety. We did, however, find positive changes in illness perceptions, which were sustained at 12-month follow-up. Dropout rates were low, suggesting MBCT was well received and regarded as an acceptable intervention by individuals with MCS. CONCLUSIONS: Overall, these results suggest that MBCT does not change overall illness status in individuals with MCS, but that MBCT positively changes emotional and cognitive representations. Possible explanations for these results are discussed.