We evaluated the effects of mindfulness on impulsivity during smoking cessation. Current methods for self-reporting formal mindfulness practice are inaccurate, so we used accelerometer-based watches to monitor formal mindfulness practice testing. In this study, we attempted to replicate the Yale trial comparing Mindfulness Training (MT) to Cognitive Behavioral Therapy (CBT) for smoking cessation. We randomized 54 subjects to CBT (n=29) or MT (n=25). First, we found no treatment effect of group on intent-to-treat point prevalence abstinence. Second, ActiWatch Score (AW) was a feasible option; however, there were limitations in its use for behavioral validation of meditation time because meditators often forgot to mark meditation end times. Interestingly, MT versus CBT completers were more likely to perceive AW as helpful (AW reminded me to practice skills) and less likely to feel it hindered their treatment goals (AW increased my craving for cigs). Finally, both groups decreased physiologic activation (heart rate and facial muscle tension) to smoking cues and craving. Secondary analyses found that capacity for non-judgment of inner experiences predicted who would quit smoking in MT but not CBT. During this trial we received additional funding from a NIDA R03 and from Harvard Medical School Department of Psychiatry Fellowship awards.