Objective. Are narcissistic athletes mentally tough? Despite the existing literature supporting the view that narcissistic grandiosity is positively related to mental toughness, no efforts have been made to understand how the agentic and antagonistic sides of narcissism are associated with mental toughness. Here we examine the effect of narcissistic admiration and rivalry on self-reported and behavioural mental toughness. Based on the different cognitive-affective-motivational pathways associated with admiration and rivalry, we hypothesized that the agentic side of narcissism (i.e., admiration) would predict greater mental toughness, whereas the antagonistic dimension of narcissism would be negatively related to mental toughness. Method. A sample of 276 elite Thai athletes completed self-report measures of narcissistic admiration and rivalry, self-esteem and mental toughness. Informant ratings of mentally tough behaviour were provided by coaches (n = 19) for a subset of athletes (n = 119). Results. Narcissistic admiration was positively associated with self and coach-ratings of mental toughness; in contrast, narcissistic rivalry was negatively associated with self and coach-ratings of mental toughness. These effects were independent of self-esteem. Conclusion. The findings stress the importance of considering the effects of different dimensions of narcissism and, contrary to previous evidence, suggest that narcissism is not universally predictive of heightened mental toughness.