Objective: Although research on the physiological and psychological factors of endurance performance has been extensive, the factors related to dropping out of ultra-trail races have not been well documented. The aim of this study was to examine psychosocial factors as predictors of dropout in ultra-trail runners. Methods: Two hundred and twenty-one volunteer athletes completed a survey that included measures of: (a) motivational variables (self-determined motivation, basic needs satisfaction, achievement goals), (b) theory of planned behavior constructs (attitudes, subjective norms, self-efficacy and intention to finish the race), and (c) coping strategies in sport. Results: The results showed that finishers had higher scores for self-efficacy and intention to finish the race than withdrawers, whereas withdrawers had higher scores for avoidance coping. Multiple logistic regression showed that the number of started and finished ultra-trail races (OR, 0.44; 95% CI 0.22–0.88; p<0.02), self-efficacy (OR, 2.03; 95% CI 1.06–3.89; p<0.04), intention to finish the race (OR, 0.34; 95% CI 0.16–0.71; p<0.004), mastery-approach goals (OR, 0.56; 95% CI 0.31–1.00; p<0.05), and coping strategies of seeking social support (OR, 0.43; 95% CI 0.26–0.71; p<0.001) were associated with a lower risk of race dropout, whereas avoidance coping strategies (OR, 2.26; 95% CI 1.46–3.52; p<0.001) were associated with an increased dropout rate. Conclusion: Interventions promoting self-efficacy constructs and specific coping strategies might contribute to preventing dropout in ultra-trailers.