This study examined the relationship between mental toughness (MT), subjectively perceived performance, and dispositional flow in a sample of 114 high-performing ironmen and standard distance triathletes (M age = 28.81 years, SD = 3.45) recruited from triathlon clubs. Participants completed the Mental Toughness Questionnaire, Dispositional Flow Scale, and self-rated subjectively perceived performance. Pearson’s correlations between these measures revealed a significant, positive relationship between global MT and subjective performance ratings (r =.62, p <.01) and between global MT and all Dispositional Flow subscales (r =.67–.81, p <.05). Linear regression analyses found that MT subscales accounted for 64% of the variance in dispositional flow. Subjective performance ratings did not add significantly to the regression model. Overall, these findings suggest that MT may contribute positively to ironman competitors’ and triathletes’ exertion of the cognitive and emotional control necessary to experience flow and perform better. We discuss these results in the context of ironman and triathlon competitions.