Depression, anxiety and eating disorders (“social-emotional disorders”) are common during adolescence/emerging adulthood, periods of intense identity development. Despite this, there are few reviews of existing research on the relationship between symptoms of these disorders and ongoing identity development. This study systematically reviewed, narratively synthesized and meta-analyzed longitudinal investigations of the relationship between identity synthesis/confusion and depression, anxiety and eating disorders symptoms during adolescence/emerging adulthood. Three databases (PsycInfo, Medline, Embase) were searched. Study quality was systematically appraised, findings were qualitatively synthesized and (where possible) meta-analyzed. 20 studies (55% “fair” quality, 45% “poor” quality) were identified, including 13,787 participants (54.2% female, mean age = 14.48 years, range 10–29 years). The narrative synthesis found evidence of bidirectional relationships between identity synthesis/confusion and depression, anxiety and eating disorder symptoms. Meta-analyses and meta-regressions of a sub-sample of studies (N = 9) indicated no significant associations between identity synthesis or confusion and anxiety or depression symptoms. More high-quality research is needed before firm conclusions can be drawn.