ImportanceAdolescents and young people have been historically understudied populations, and previous studies indicate that during epidemics, these populations, especially in low- and middle-income countries (LMICs), are at high risk of developing mental disturbances.ObjectiveTo identify the existing evidence regarding the association of mental health with outbreaks of the influenza A (H1N1), Zika, Ebola, and SARS-CoV-2 virus in exposed youth and adolescents in LMICs.Evidence ReviewAcross 6 databases (Embase, Cochrane Library, PubMed, PsycINFO, Scopus, and Web of Science), the mental health outcomes of adolescents and youth (aged 10-24 years) associated with 4 major pandemic outbreaks from January 2009 to January 2021 in LMICs were reviewed. A group of 3 authors at each stage carried out the screening, selection, and quality assessment using Joanna Briggs Institute checklists. The social determinants of adolescent well-being framework was used as a guide to organizing the review.FindingsA total of 57 studies fulfilled the search criteria, 55 related to the SARS-CoV-2 (COVID-19) pandemic and 2 covered the H1N1 influenza epidemics. There were no studies associated with Zika or Ebola outbreaks that met screening criteria. The studies reported high rates of anxiety and depressive symptoms among adolescents, including posttraumatic stress disorder, general stress, and health-related anxiety. Potential risk factors associated with poor mental health outcomes included female sex; home residence in areas with strict lockdown limitations on social and physical movement; reduced physical activity; poor parental, family, or social support; previous exposure to COVID-19 infection; or being part of an already vulnerable group (eg, previous psychiatric conditions, childhood trauma, or HIV infection).Conclusions and RelevanceResults of this systematic scoping review suggest that the COVID-19 pandemic and H1N1 epidemic were associated with adverse mental health among adolescents and youth from LMICs. Vulnerable youth and adolescents may be at higher risk of developing mental health–related complications, requiring more responsive interventions and further research. Geographically localized disease outbreaks such as Ebola, Zika, and H1N1 influenza are highly understudied and warrant future investigation.