<p>Peri-adolescence, the developmental window surrounding pubertal onset, is a critical period for the emergence and escalation of anxiety symptoms, making accurate assessment essential. While parent-reports are typically prioritized in childhood and youth self-reports in later adolescence, these perspectives often diverge during peri-adolescence, and such discrepancies are inconsistently linked to age. This study tested whether pubertal stage, rather than chronological age, accounts for differences between parent- and youth-reported anxiety, aiming to clarify how anxiety is experienced and perceived during this sensitive developmental transition. Two-hundred peri-adolescents (ages 10-13) and their parents completed clinical interviews, anxiety rating scales, and the Pubertal Development Scale. Mixed-effects models tested whether discrepancies varied as a function of pubertal stage, controlling for age. We also explored the utility of Principal Components Analysis (PCA) to extract shared variance across informants into a single multi-informant anxiety score. More advanced pubertal stage was associated with greater discrepancies in anxiety reports, driven by higher youth self-reports and stable parent ratings—especially among clinically anxious youth (n = 94). PCA identified a single cross-informant factor that captured shared variance and improved prediction of clinical severity and functioning. Puberty, rather than age, plays a key role in how caregivers and adolescents report on anxiety symptoms. These findings underscore the need to account for pubertal stage in peri-adolescent assessment and support the utility of dimensional, developmentally sensitive approaches for integrating multi-informant data.</p>