["Criminology, Volume 60, Issue 3, Page 538-575, August 2022. ", "\nAbstract\nHarsh prison conditions have been widely examined for their effects on the mental health of incarcerated people, but few studies have examined whether mental health status exposes individuals to harsh treatment in the penal system. With prisoners confined to their cells for up to 23 hours each day, often being denied visitors or phone calls, solitary confinement is an important case for studying harsh treatment in prisons. Routinely used as punishment for prison infractions, solitary confinement may be subject to the same forces that criminalize the mentally ill in community settings. Analyzing a large administrative data set showing admissions to solitary confinement in state prison, we find high rates of punitive isolation among those with serious mental illness. Disparities by mental health status result from the cumulative effects of prison misconduct charges and disciplinary hearings. We estimate that those with serious mental illness spend three times longer in solitary confinement than similar incarcerated people with no mental health problems. The evidence suggests the stigma of dangerousness follows people into prison, and the criminalization of mental illness accompanies greater severity of incarceration.\n"]