This study examined the relationship of sports experience with ego development. A questionnaire was used to assess experience of Crisis, Exploration, and Commitment in the issues of Athletic Performance and of Being a Teammate in 782 adolescent Japanese athletes (423 boys, M age = 15.2 yr.; 359 girls, M age = 15.0 yr.). Their Ego Levels were assessed using the Washington University Sentence Completion Test. Correlations indicated that scores on Crisis, Exploration, and Commitment in the issues of Athletic Performance and Being a Teammate were generally associated with Ego Development. Multiple regression analyses indicated that, for boys, the issue of Athletic Performance was closely associated with Ego Development, while for girls, the issue of Being a Teammate was closely associated with Ego Development. Sports experience with crisis, exploration, and commitment may be related to accommodation, which is, in turn, related to ego development. The sex differences on issues related to ego development may be associated with differences in sex-role development for boys and girls.