A significant number of prisoners experience mental health problems, and adequate social support is one way that facilitates better mental health. Yet, by being incarcerated, social support, particularly family support, is likely to be strained or even negative. In this study, we examine whether familial support—either positive or negative—in-prison and after release affects mental health outcomes post-release. Using the Serious and Violent Offender Reentry Initiative (SVORI) dataset, we regress post-release mental health on in-prison familial support, post-incarceration familial support, and changes in familial support. We find that while in-prison family support does not affect mental health, post-release familial support does. Also, experiencing an increase in negative familial support is associated with lower post-incarceration mental health. We conclude with a discussion of policies which may facilitate better familial support environments.