Developmental trajectories of internalizing and externalizing behaviors in LGBTQ+ youth in the ABCD Study.

LGBTQ+ youth experience elevated internalizing distress, yet research on externalizing behaviors and their early development remains limited. This study examined trajectories of internalizing and externalizing behaviors from childhood into adolescence using data from the Adolescent Brain Cognitive Development Study (N = 11,878 at baseline, Mage = 9.80 years, SD = 0.62, 63.3% White, 52.2% male), assessed four times at ages 9/10, 10/11, 11/12, and 12/13. Linear mixed-effects models tested differences between LGBTQ+ and non-LGBTQ+ youth and among disaggregated sexual and gender identity subgroups. In the omnibus comparison, LGBTQ+ youth showed higher internalizing behaviors at age 9/10 (β = 0.18, 95% CI [0.13, 0.22]) and a more rapid increase into adolescence (β = 0.10 [0.08, 0.11]) than non-LGBTQ+ peers, along with higher externalizing behaviors at age 9/10 (β = 0.18 [0.13, 0.23]) and a smaller increase over time (β = 0.03 [0.01, 0.04]; all ps < .001). Trajectories were substantially heterogeneous across subgroups, with the omnibus pattern disproportionately driven by youth holding multiple minoritized identities, who showed the most rapid increases in both domains. Mental health disparities among LGBTQ+ youth thus emerge by late childhood, persist into early adolescence, and are most acute among multiply-minoritized youth.