The self-equilibrium hypothesis underlines the importance of having a strong core self, which is defined as a high and developmentally stable self-concept. This study tested this hypothesis in relation to body image (BI) trajectories in a sample of 1,006 adolescents (M[subscript age] = 12.6, including 541 males and 465 females) across a 4-year period. The results supported the self-equilibrium hypothesis among 3 profiles of adolescents, all characterized by matching BI levels and stability: (a) "High" (48.0%); (b) "Increasing" (34.1%); and (c) "Decreasing" (17.9%). Boys presented higher levels of BI, and the quality of relationships with peers and parents predicted initially more desirable trajectories across gender. By the end of the study, more positive academic outcomes were associated with the "Decreasing" profile, lower internalizing problems with the "High" profile, and lower externalizing problems with the "High" and the "Increasing" profiles.