Characterize the prevalence of chronic physical illness types and mental illness and their comorbidity among adolescents and young adults (AYA) and assess the association of comorbidity on hospital utilization.


This study features a population-level sample of 61 339 insurance-eligible AYA with an analytic sample of 49 089 AYA (aged 12–21) in Vermont’s 2018 all-payer database. We used multiple logistic regressions to examine the associations between physical illness types and comorbid mental illness and emergency department (ED) use and inpatient hospitalization.


The analytic sample was 50% female, 63% Medicaid, and 43% had ≥1 chronic illness. Mental illness was common (31%) and highly comorbid with multiple physical illnesses. Among AYA with pulmonary illness, those with comorbid mental illness had 1.74-times greater odds (95% confidence interval [CI]: 1.49–2.05, P ≤.0005) of ED use and 2.9-times greater odds (95% CI: 2.05–4.00, P ≤.0005) of hospitalization than those without mental illness. Similarly, comorbid endocrine and mental illness had 1.84-times greater odds of ED use (95% CI: 1.39–2.44, P ≤.0005) and 2.1-times greater odds of hospitalization (95% CI: 1.28–3.46, P = .003), comorbid neurologic and mental illness had 1.36-times greater odds of ED use (95% CI: 1.18–1.56, P ≤.0005) and 2.4-times greater odds of hospitalization (95% CI: 1.73–3.29, P ≤.0005), and comorbid musculoskeletal and mental illness had 1.38-times greater odds of ED use (95% CI: 1.02–1.86, P = .04) and 2.1-times greater odds of hospitalization (95% CI: 1.20–3.52, P = .01).


Comorbid physical and mental illness was common. Having a comorbid mental illness was associated with greater ED and inpatient hospital utilization across multiple physical illness types.

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