Early pubertal timing has consistently been associated with internalizing psychopathology in adolescent girls. Here, we aimed to examine whether the association between timing and mental health outcomes varies by measurement of pubertal timing and internalizing psychopathology, differs between adrenarcheal and gonadarcheal processes, and is stronger concurrently or prospectively. We assessed 174 female adolescents (age 10.0-13.0 at Time 1) twice, with an 18-month interval. Participants provided self-reported assessments of depression/anxiety symptoms and pubertal development, subjective pubertal timing, and date of menarche. Their parents/guardians also reported on the adolescent's pubertal development and subjective pubertal timing. We assessed salivary dehydroepiandrosterone (DHEA), testosterone, and estradiol levels and conducted clinical interviews to determine the presence of case level internalizing disorders. From these data, we computed 11 measures of pubertal timing at both time points, as well as seven measures of internalizing psychopathology, and entered these in a Specification Curve Analysis. Overall, earlier pubertal timing was associated with increased internalizing psychopathology. Associations were stronger prospectively than concurrently, suggesting that timing of early pubertal processes might be especially important for later risk of mental illness. Associations were strongest when pubertal timing was based on the Tanner Stage Line Drawings and when the outcome was case-level Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) depression or Hierarchical Taxonomy of Psychopathology (HiTOP) distress disorders. Timing based on hormone levels was not associated with internalizing psychopathology, suggesting that psychosocial mechanisms, captured by timing measures of visible physical characteristics might be more meaningful determinants of internalizing psychopathology than biological ones in adolescent girls. Future research should precisely examine these psychosocial mechanisms. (PsycInfo Database Record (c) 2022 APA, all rights reserved).