Every day, between 41,000 to 48,000 inmates, many of them seriously mentally ill (SMI) inmates, live in solitary confinement (solitary), which represents the most severe punishment that inmates can face aside from execution. With solitary, prison officials segregate inmates from the general prison population and deprive them of human contact and sensory stimulation for disciplinary or security reasons. Modern day research has confirmed its negative mental health impact, especially on SMI in-mates, which can lead to suicide.

The Supreme Court’s traditional prison conditions jurisprudence grounds itself in the Eighth Amendment’s cruel and unusual punishments clause and the evolving standards of decency. It protects against the substantial risk of serious harm to which prison officials are deliberately indifferent. SMI inmates in solitary often advance two claims, that officials impose inhumane prison conditions and provide inadequate mental health care. Some cases, including a few class actions, have declared placing SMI inmates in solitary unconstitutional and denounced ineffective screening that led to placing SMI inmates in solitary. However, be-fore overcoming their customary deference to prison officials, courts required egregious levels of harm.

The courts’ proportionality review of sentences, also based on the Eighth Amendment and evolving standards of decency, offers an alternative doctrine that better equips courts to overcome their customary deference to prison officials. Courts have used proportionality review, for ex-ample, to ban the execution of the intellectually disabled and the doctrine can likewise lead to a broad ban on placing SMI inmates in solitary. Practically speaking, this entails considering the weight of current policy and the degree to which placing SMI inmates in solitary satisfies penological goals, to wit, retribution, incapacitation, deterrence, and rehabilitation. Also, professional organizations, international authorities, and Colorado, a good example of solitary reform, all support a broad ban on placing SMI inmates in solitary.