This study investigated the relationship between cognitive development level and the ideal self in adolescence, sampling 223 male and female 12- and 13-, and 15- and 16-year-old working and middle class English comprehensive school students, hypothesizing that maturity of the ideal self would be related to cognitive development. Correlations between cognitive developmental total score and ideal self score were significant for the whole sample and for both age groups. Regression analysis showed cognitive development score to be the major significant predictor of ideal self score at both age levels, with sex contributing additionally at the older age level.