In addition to housing, employment, and registration restrictions, sex offenders have been subjected to electronic monitoring with the idea that they may be either surveilled or deterred from committing additional crime. This study evaluated the supervision costs of placing high-risk sex offender parolees on Global Positioning Satellite (GPS) monitoring as part of a pilot program by the California Department of Corrections and Rehabilitation. Using a quasiexperimental design, the study tracked parolees’ costs of supervision and their parole violations for 1 year. GPS was not cost-effective; the overall cost of parolees on GPS was greater than parolees not on the monitoring, the two groups committed similar parole violations, and parolees on GPS were retained on parole longer.