© 2016 Academic Pediatric Association Objective Recent policy initiatives aiming to reduce firearm morbidity focus on mental health and illness. However, few studies have simultaneously examined mental health and behavioral predictors within families, or their longitudinal association with newly acquiring a firearm. Methods Population-based, longitudinal survey of 4251 parents of fifth-grade students in 3 US metropolitan areas; 2004 to 2011. Multivariate logistic models were used to assess associations between owning or acquiring a firearm and parent mental illness and substance use. Results Ninety-three percent of parents interviewed were women. Overall, 19.6% of families reported keeping a firearm in the home. After adjustment for confounders, history of depression (adjusted odds ratio [aOR], 1.36; 95% confidence interval [CI], 1.04–1.77), binge drinking (aOR 1.75; 95% CI, 1.14–2.68), and illicit drug use (aOR 1.75; 95% CI, 1.12–2.76) were associated with a higher likelihood of keeping a firearm in the home. After a mean of 3.1 years, 6.1% of parents who did not keep a firearm in the home at baseline acquired one by follow-up and kept it in the home (average annual likelihood = 2.1%). No risk factors for self-harm or other violence were associated with newly acquiring a gun in the home. Conclusions Families with risk factors for self-harm or other violence have a modestly greater probability of having a firearm in the home compared with families without risk factors, and similar probability of newly acquiring a firearm. Treatment interventions for many of these risk factors might reduce firearm-related morbidity.