Background <p>Alexithymia is a form of maladaptive emotion processing characterized by difficulty identifying and communicating emotions. Such impairments are risk factors for both internalizing and externalizing behaviors. Extant research suggests that biological sex may contribute to heterogeneous patterns of outcomes. However, sex-specific effects of alexithymia on internalizing and externalizing outcomes have yet to be examined together. Moreover, the nature of associations between alexithymia and proactive versus reactive aggression remains unclear, as prior studies have yielded mixed results. Further, there is limited research on how these relations manifest in detained youth, who are at increased risk for alexithymia and psychological maladjustment.</p> Objective <p>This study investigated: (a) associations between alexithymia and adjustment outcomes among detained youth, and (b) whether these associations vary in strength in a sex-specific manner.</p> Methods <p>Youth (<i>N</i> = 111, <i>M</i>_age = 15.5&#xa0;years) residing in a detention facility reported alexithymic traits, as well as symptoms of anxiety and proactive and reactive aggression.</p> Results <p>Consistent with prior research, overall alexithymia independently contributed to higher anxiety and reactive aggression. Subscale analyses revealed that difficulty identifying feelings was uniquely associated with anxiety and reactive aggression, difficulty describing feelings with anxiety and proactive aggression, and externally-oriented thinking with anxiety only. Contrary to our hypotheses, sex did not moderate associations between alexithymia and adjustment outcomes.</p> Conclusions <p>These findings clarify the distinct contributions of various facets of alexithymia to internalizing and externalizing outcomes among detained youth.</p>