OBJECTIVES: Mindfulness-based approaches may benefit patients with chronic tinnitus, but most evidence is from small studies of nonstandardized interventions, and there is little exploration of the processes of change. This study describes the impact of mindfulness-based cognitive therapy (MBCT) in a "real world" tinnitus clinic, using standardized MBCT on the largest sample of patients with chronic tinnitus to date while exploring predictors of change. DESIGN: Participants were 182 adults with chronic and distressing tinnitus who completed an 8-week MBCT group. Measures of tinnitus-related distress, psychological distress, tinnitus acceptance, and mindfulness were taken preintervention, postintervention, and at 6-week follow-up. RESULTS: MBCT was associated with significant improvements on all outcome measures. Postintervention, reliable improvements were detected in tinnitus-related distress in 50% and in psychological distress in 41.2% of patients. Changes in mindfulness and tinnitus acceptance explained unique variance in tinnitus-related and psychological distress postintervention. CONCLUSIONS: MBCT was associated with significant and reliable improvements in patients with chronic, distressing tinnitus. Changes were associated with increases in tinnitus acceptance and dispositional mindfulness. This study doubles the combined sample size of all previously published studies. Randomized controlled trials of standardized MBCT protocols are now required to test whether MBCT might offer a new and effective treatment for chronic tinnitus.