Posttraumatic stress disorder (PTSD) and depressive symptoms have been associated with poorer health‐related quality of life in adolescents after general traumatic injuries; few studies have examined the broader construct of postinjury quality of life (QOL). We evaluated the impact of traumatic injury on adolescent QOL and examined factors that potentially contribute to poorer outcomes, using the Youth Quality of Life Instrument–Research Version as the outcome measure. Data were collected within 30 days postinjury and 2, 5, and 12 months postinjury. Mixed‐model regression (MMR) was used for the main analyses. Participants (N = 204) were drawn from a prospective cohort study of 12–18‐year‐olds admitted to a Level 1 trauma center (n = 108) and healthy participants from a local cross‐sectional study (n = 116); study group participants were significantly older. The initial MMR indicated that female adolescents had significantly lower QOL, B = −2.69, 95% CI [−4.68, −0.70], and were more likely to score above the cutoffs for PTSD (19.1% vs. 2.0%), χ2(1, N = 381) = 34.6, p < .001, or depression (32.8% vs. 14.0%), χ2(1, N = 381) = 18.7, p < .001, on post hoc analyses. Adolescents with mental health conditions in the year postinjury had significant QOL deficits without predicted improvements toward baseline, PTSD: B = −10.05, 95% CI [−15.29, −4.81]; depression: B = −18.00, 95% CI [−21.69, −14.31]. These findings highlight the importance of ongoing mental health monitoring and care for adolescents, particularly female adolescents, following traumatic injury even when physical recovery appears complete.