BACKGROUND The surge in adolescent smartphone use has coincided with the rise in the adolescent mental health crisis, raising public health concerns. Moving beyond the traditional focus on screen time, this study examined the association between smartphone attachment and mental health among adolescents. METHODS Data were analyzed from 137 community-dwelling adolescents (aged 16.5-18 years). Smartphone attachment was measured by the Mobile Phone Involvement Questionnaire (MPIQ). Patient Reporting Outcome Measures (PROMIS) pediatric short forms were used to measure anxiety, depression, sleep disturbance, and general health. t-tests and ANOVAs compared anxiety and depression scores between groups above and below the MPIQ threshold for moderate-to-severe attachment. Multivariable regressions estimated associations between smartphone attachment and mental health outcomes, adjusting for demographics and health factors. RESULTS Participants were a mean age of 17.7 ± 0.6 years, 51.1% female, and 79.6% White and 96.4% non-Hispanic. Mean MPIQ score was 28.90 ± 8.85, with females scoring higher than males (30.5 vs. 27.2, p = 0.03). Adolescents above the MPIQ threshold for moderate-severe attachment ( ≥ 32) reported significantly higher anxiety (52.9 vs. 46.3, p < 0.001) and depression (51.4 vs. 46.3, p = 0.002). In regression models, MPIQ scores were significantly associated with anxiety (adj. ß = 0.26, p < 0.01, CI = [0.099, 0.41]) and depression (adj. ß = 0.15, p < 0.05, CI = [0.16, 0.28]), adjusting for demographics and health factors. CONCLUSIONS Findings highlight a clinical concern for adolescents with elevated smartphone attachment, particularly among females. Targeted interventions are needed to prevent worsening mental health related to smartphone attachment.