Prolonged solitary confinement is inconsistent with international minimum rules for the treatment of prisoners and may constitute cruel, inhuman, or degrading treatment. In a series of recent cases, appellate courts in Canada have curtailed the use of prolonged solitary confinement in prisons on the basis that such detention is “grossly disproportionate” and “cruel and unusual.” But these judgments in the penal context have not resulted in comparable regulation of seclusion in forensic psychiatric hospitals. Seclusion in these contexts is often comparable to solitary confinement in prison and carries with it the same serious risks of lasting harm. This article comparatively reviews the legislative and policy framework that regulates the use of seclusion in different provinces in Canada. The article argues that case law on prolonged solitary confinement in the penal context has application to the forensic psychiatric context and that a failure to more closely regulate the use of seclusion may render this type of mental health legislation and treatment unconstitutional.