This study aimed to examine the impact of quantity of mindfulness meditation practice on the outcome of psychiatric symptoms following Mindfulness-based Cognitive Therapy (MBCT) for those diagnosed with bipolar disorder. Meditation homework was collected at the beginning of each session for the MBCT program to assess quantity of meditation practice. Clinician-administered measures of hypo/mania and depression along with self-report anxiety, depression and stress symptom questionnaires were administered pre-, post-treatment and at 12-month follow-up. A significant correlation was found between a greater number of days meditated throughout the 8-week trial and clinician-rated depression scores on the Montgomery-Åsberg Depression Rating Scale at 12-month follow-up. There were significant differences found between those who meditated for 3 days a week or more and those who meditated less often on trait anxiety post-treatment and clinician-rated depression at 12-month follow-up whilst trends were noted for self-reported depression. A greater number of days meditated during the 8-week MBCT program was related to lower depression scores at 12-month follow-up, and there was evidence to suggest that mindfulness meditation practice was associated with improvements in depression and anxiety symptoms if a certain minimum amount (3 times a week or more) was practiced weekly throughout the 8-week MBCT program.