OBJECTIVE: The aim of this study was to determine whether advanced puberty at age 9 and 10 years, relative to that in same-aged peers, predicts current and/or new-onset self-injurious thoughts and behaviors (SITBs). New predictors of SITBs in preadolescence are urgently needed to address this escalating public health crisis of youth self-harm and suicidality. METHOD: Data from the baseline, 1-year, and 2-year waves of the Adolescent Brain and Cognitive Development Study were used. Bayesian mixed-effects models were estimated for test and replication split halves, and tested whether relatively advanced youth-reported pubertal development at 9 or 10 years predicted SITBs (suicidal ideation, suicide attempts, and non-suicidal self-injury) as reported by preadolescents (each wave) and their caregiver (baseline, 2-year follow-up) in a computerized version of the Kiddie Schedule for Affective Disorders and Schizophrenia (KSADS). Preadolescents with baseline self-reported puberty, KSADS (N = 8,708
44.6% female
60.8% White non-Hispanic), and demographic information were included. RESULTS: Baseline preadolescent-reported puberty predicted the presence of any SITB before or at baseline (odds ratio = 1.50, 95% credible interval = 1.23-1.85) and the new-onset SITBs between baseline and 2-year follow-up in preadolescents SITB-naive at baseline (odds ratio = 2.26, 95% credible interval = 1.66-3.21). CONCLUSION: Preadolescents reporting relatively advanced puberty were more likely to have experienced SITBs and, if SITB naive, were more likely to experience the onset of SITBs across the following 2 years. Findings were not explained by child psychopathology or other familial and psychosocial factors known to predict SITBs. Screening preadolescents for advanced puberty at ages 9 and 10 years and applying targeted suicide screening for those youth showing advanced puberty should be considered in primary care and mental health settings.