Self-esteem is a personality trait utilized to support the diagnosis of several psychological conditions. With this study we investigate the potential that computer games can have in assessing self-esteem. To that end, we designed and developed a platformer game and analyzed how in-game behavior relates to Rosenberg's Self-Esteem Scale. We examined: i) how a player's self-esteem influences game performance, ii) how a player's self-esteem generally influences in-game behavior iii) the possible game mechanics that assist in inferring a player's self-esteem. The study was conducted in two phases (N=98 and N=85). Results indicate that self-esteem does not have any impact on the player's performance, on the other hand, we found that players' self-evaluation of game performance correlates with their self-esteem.