This article examines the psychological consequences of short- and long-term solitary confinement for prisoners in the United States subjected to administrative or disciplinary segregation. Particular attention is paid to the use of secure housing units, alternatively known as control units or supermax units. These correctional entities allow for the isolation of convicts under conditions that offer little sensory stimulation and minimal opportunities for interaction with other people. The circumstances typically found in these units and the heightened potential for the abuse of prisoners are described. The connections between internment and mental illness-as well as isolation and race, gender, and class-are explored. A set of recommendations for the reform of secure housing is presented.