In response to rising pharmacy costs in the Iowa Department of Corrections prison system, a retrospective analysis of psychiatric drug use and expenditures was performed for fiscal years 1990 through 2000. Population-adjusted changes in use and expenditures over time were analyzed in aggregate and by drug class. Expenditures for psychiatric drugs increased 28-fold from $7,974 in 1990 to $381,893 in 2000, or from $291 to $8,138 per 100 inmates, while use increased fivefold. The use of antipsychotics remained relatively constant, but expenditures increased ninefold. In contrast, both use of and expenditures for antidepressants increased tremendously, from $215 to $1,929 per 100 inmates.