This exploratory research examines supermax confinement in the United States. An examination of counts of supermax institutions and inmates from 2001-2004 produced by the American Correctional Association and an examination of Criminal Justice Institute data found that different procedures made it difficult to compare numbers across states. Certain states produced incorrect figures about the number of supermax prisons and inmates because of reporting and/or recording errors. This study found, in short, that disagreements about definitions, changing policies and court decisions, reporting and recording errors, and different counting procedures have led to a lack of reliable and valid data on supermax issues. These findings indicate that researchers attempting to examine, or collect data on, supermax issues on the macrolevel (e.g., across states) face important difficulties. This article accounts for this confusion, discusses policy implications that may result from this confusion, and concludes with suggestions for future research.