The purpose of this study was to examine motivational correlates of mentally tough behaviours among adolescent tennis players.Two-phase study, involving the development of an informant-rated measure of mentally tough behaviours, followed by a cross-sectional survey including athlete and parent assessments of study variables.In Phase One, 17 adult, high-performance tennis coaches and 20 athletes participated in focus group interviews. Four scholars with expertise in performance psychology also completed a short, online survey. In Phase Two, a total of 347 adolescent tennis players (n males =184; n females =163) aged 12–18 years (M=13.93, SD=1.47) and one respective parent took part in this study. An online multisection survey containing dimensions of passion, inspiration, fear of failure, and mentally tough behaviours was completed. Athletes self-reported all motivational variables, whereas parents rated their child solely on mentally tough behaviours.Structural equation modelling revealed that harmonious passion (β=.26, p<.01) and frequency of inspiration (β=.32, p<.001) were associated with significantly higher levels of mentally tough behaviours. In contrast, fear of failure (β=−.32, p<.001) and obsessive passion (β=−.15, p<.01) were inversely related to mentally tough behaviours. Inspiration intensity was not significantly associated with mentally tough behaviour (β=.13, p=.21).Motivational variables that are dispositional in nature, contextualised and contingent upon features of the environment, and concern one's identity are important considerations for understanding mentally tough behaviours.