The purpose of the present investigation was to evaluate the long-term effects of mindful sport performance enhancement (MSPE), a program designed to improve athletic performance and psychological aspects of sport. One-year follow-up assessments were conducted on archers, golfers, and long-distance runners (N = 25) who attended Kaufman, Glass, and Arnkoff’s (2009) and De Petrillo, Kaufman, Glass, and Arnkoff’s (2009) MSPE workshops. Across the athlete groups, participants reported significant increases in the ability to act with awareness (an aspect of trait mindfulness) and overall trait mindfulness from pretest to follow-up, along with significant decreases in task-related worries and task-irrelevant thoughts (both aspects of cognitive interference during sport). The long-distance runners exhibited significant improvement in their mile times from pretest to follow-up, with significant correlations between change in runners’ performance and trait variables. Results suggest that MSPE is a promising intervention associated with long-term changes in trait variables that may contribute to optimal athletic performance.