This research examined longitudinal associations between youth physical-mental multimorbidity and psychological distress before and during the COVID-19 pandemic; assessed the contextual impact of the pandemic on these associations; and, investigated potential moderating factors. The Multimorbidity in Youth across the Life-course, an ongoing study of youth aged 2–16 years (mean 9.4; 46.9% female) with physical illness, was used as the sampling frame for this COVID-19 sub-study, in which 147 parent-youth dyads participated. Psychological distress was measured using the Kessler-6 (K6). Multimorbidity was associated with higher pre-pandemic, but not with intra-pandemic distress. Disability moderated pre-pandemic distress—multimorbidity was associated with higher K6 among youth with high disability, but not among youth with low disability. Age moderated intra-pandemic distress—multimorbidity was associated with higher K6 in older youth, but not among younger youth.
