At the end of 1998 some 20,000 prisoners or 1.8 percent of all those serving sentences of a year or more in State and Federal prisons were accommodated in supermax facilities. Most such facilities were newly constructed although some were retro-fitted existing buildings either instead of or in addition to new buildings. In such facilities, prisoners loosely defined as “the worst of the worst” are kept in near total lock-down situations, sometimes for very long periods and often without clear entry and exit criteria, ostensibly to protect staff, other prisoners and the public. On the basis of comparisons with European experience, where resort to such levels of restrictive custody has typically been on a much smaller and more time limited scale, and has involved little new building, the article questions whether supermax custody in the United States is either a necessary or a proportionate response to the problems actually experienced. Table, notes, references