Achieving a clear view of one’s personality is a challenging but crucial developmental task during adolescence, which has enduring influences. This task might be harder if significant others see individuals differently from how the adolescents see themselves. Supporting this, the looking-glass-self theory suggests that significant others constitute a social mirror into which the individual gazes to form his/her self-view. The present study was the first to longitudinally examine whether self–other agreement in personality during adolescence (i.e., self–parent and self–friend agreement at age 12 and self–mother and self–father agreement at age 17) promote self-esteem development from age 17 to 29 years (N =186, 53% boys). Results for girls consistently confirmed the hypothesized beneficial effect of self–parent agreement, while the picture was more complicated for boys. That is, for girls, self–parent agreement at age 12 and age 17 both predicted steeper increases in self-esteem. For boys, steeper self-esteem development was predicted by higher self–parent agreement at age 12, but unexpectedly, also by lower self–parent agreement at age 17. All these results remained after controlling for (self-rated) personality. Moreover, self–friend agreement did not show any effects on self-esteem development, suggesting that the influence of peers’ convergence with self-views during early adolescence may not be as prominent as parents’. Results are discussed from the perspective of self-view formation and maintenance during adolescence and young adulthood. The present study sheds light on the longitudinal effect of one’s own view of personality being shared by important others on self-esteem development.