Bipolar disorder is associated with impairments in cognition, including difficulties in executive functioning, even when patients are euthymic (neither depressed nor manic). The purpose of this study was to assess changes in self-reported cognitive functioning in patients with bipolar disorder who participated in an open pilot trial of mindfulness-based cognitive therapy (MBCT). Following MBCT, patients reported significant improvements in executive functioning, memory, and ability to initiate and complete tasks, as measured by the Behavior Rating Inventory of Executive Function (BRIEF) and the Frontal Systems Behavior Scale (FrSBe). Changes in cognitive functioning were correlated with increases in mindful, nonjudgmental observance and awareness of thoughts, feelings, and sensations, and were not associated with decreases in depression. Improvements tended to diminish after termination of treatment, but some improvements, particularly those in executive functioning, persisted after 3 months. These results provide preliminary evidence that MBCT may be a treatment option that can be used as an adjunct to medication to improve cognitive functioning in bipolar disorder.