Objective: This longitudinal study investigated the predictors of and changes in psychological trauma during the COVID-19 pandemic. Method: Participants included 236 adolescents (130 males; M age = 16.74 years in spring 2020; 49.6% diagnosed with attention-deficit hyperactivity disorder; 16.1% diagnosed with an anxiety or depressive disorder) in the United States who completed online questionnaires at four timepoints (spring 2020, summer 2020, fall 2020, spring 2021). Results: Repeated measures ANOVA showed that psychological trauma was highest during stay-at-home orders in spring 2020, and decreased for a majority of adolescents by the summer of 2020. However, [approximately]20% of adolescents exhibited moderate-to-clinical levels of psychological trauma at each timepoint. Four groups were identified based on the presence of psychological trauma symptoms: (1) "resilient group" (normal range across all timepoints; 60.6%), (2) "moderate fluctuating group" (moderate range at one or more timepoints; 18.2%), (3) "severe fluctuating group" (clinical range at one or more timepoints; 14.0%), and (4) "chronic psychological trauma group" (moderate or clinical range across all timepoints; 7.2%). Females, adolescents with pre-existing internalizing disorders, and participants whose families were most impacted by the pandemic were more susceptible to experiencing psychological trauma symptoms. Conclusions: Findings highlight at-risk populations and suggest that the COVID-19 pandemic resulted in psychological trauma symptoms for approximately 20% of adolescents at some point during the first year of the pandemic. There is critical need to provide mental health services to adolescents, such as through school-based services, to reduce the negative long-term psychological impact of the pandemic. [This paper was published in "Psychological Trauma: Theory, Research, Practice, and Policy."]