The research used the Federal Prison System Custody Determination instrument with a sample of the Arizona inmate population to simulate the classification process. The simulation showed that 59 percent of the Arizona inmates were assigned to medium custody, compared to only 21 percent using the Federal model. The Department assigned only 13 percent to minimum custody, compared to the 47 percent suggested by the Federal model. However, moderate underclassification occurred for maximum custody. Approximately 26 percent of the sample was initially assessed as maximum custody, compared to more than 30 percent under the Federal model. The main reason for the high number of medium-custody assignments appears to be the large number of medium custody housing units in the Arizona system. Results indicate the need for more minimum and maximum security beds and the use of an objective classification system. Additional recommendations, tables, figures, and appended Arizona classification codebook and related materials.