The long-term consequences of exposure to firearm injury-including suicide, assault, and mass shootings-on children's mental and physical health is unknown. Using PRISMA-ScR guidelines, we conducted a scoping review of four databases (PubMed, Scopus, PsychINFO, and CJ abstract) between January 1, 1985 and April 2, 2018 for articles describing long-term outcomes of child or adolescent firearm injury exposure (n = 3582). Among included studies (n = 31), most used retrospective cohorts or cross-sectional studies to describe the correlation between firearm injury and post-traumatic stress. A disproportionate number of studies examined the effect of mass shootings, although few of these studies were conducted in the United States and none described the impact of social media. Despite methodologic limitations, youth firearm injury exposure is clearly linked to high rates of post-traumatic stress symptoms and high rates of future injury. Evidence is lacking on best practices for prevention of mental health and behavioral sequelae among youth exposed to firearm injury. Future research should use rigorous methods to identify prevalence, correlates, and intervention strategies for these at-risk youth.