OBJECTIVE: To estimate the risk of insurance instability following firearm injury. BACKGROUND: Health insurance instability is associated with negative clinical outcomes. After nonfatal firearm injury, continuity of health care is particularly important given substantially increased physical, mental, and rehabilitative needs and related healthcare spending. METHODS: Using 2007-2022 commercial insurance claims data, we studied 3,653 survivors and 17,422 matched controls to investigate the risk of health insurance instability associated with firearm injury. Participants were matched on age, Diagnostic Cost Group risk score, year, month, plan type, drug coverage, sex, metropolitan statistical area, state, and enrollee category. RESULTS: The mean age of survivors was 30.5 years, 83.7% were male, 39.2% were primary enrollees, with observable characteristics closely balanced between exposed and control groups after matching. Within 1 year of injury, 36.1% of survivors experienced insurance instability compared with 28.1% of matched controls-an attributable risk of 8.0 (95% CI: 5.8, 10.1) and adjusted hazard ratio of 1.34 (95% CI: 1.26, 1.42). For survivors with more severe injuries, 37.3% experienced insurance instability compared with 27.6% of matched controls-an attributable risk of 9.8 (95% CI: 6.7, 12.9) and adjusted hazard ratio of 1.43 (95% CI: 1.31, 1.56). On average, firearm-injured primary enrollees experiencing insurance instability provided coverage for 0.84 dependents (spouses and children) at the time of their insurance status change. CONCLUSIONS: Firearm injury was followed by increased insurance instability among survivors, with increased risk following more severe injuries. Insurance instability may disrupt care and shift costs to the public through public insurance enrollment and uncompensated care for the uninsured.