Objective: To investigate the relationship between mental toughness, sport injury beliefs, pain, and adherence toward a sport injury rehabilitation program. Design: A prospective design was employed that evaluated adherence over the entire rehabilitation period. Participants: 70 patients undertaking a sport injury rehabilitation program for a tendonitis related injury. Main Outcome Measures: Adherence was measured using self report measures of clinic and home based rehabilitation alongside attendance. Results: No association was found between mental toughness and coping appraisals, although high mentally tough individuals displayed more positive threat appraisals and were better able to cope with pain than their less mentally tough counterparts. Greater attendance at rehabilitation sessions was displayed by more mentally tough individuals; however, more positive behavior during clinic rehabilitation was characterized by low mental toughness. Conclusions: Despite the 0benefits of being mentally tough, sports medicine providers need to be aware that a high degree of mental toughness may have negative consequences upon rehabilitation behavior and subsequently recovery outcomes.