Despite the increasing number of high-risk sex offenders (HRSOs) who are being placed on electronic monitoring programs, little is known about how effective these programs are in increasing offender compliance and reducing recidivism. This study integrated outcome, cost, and process evaluation components to assess the impact of the California Department of Corrections and Rehabilitation’s global positioning system (GPS) supervision program. The study population was drawn from all HRSOs released from prison and residing in California between January 2006 and March 2009. The sample included 516 subjects equally divided into a treatment group, placed on GPS monitoring, and control group, not placed on GPS monitoring. The effectiveness of the program was assessed using an intent-to-treat approach with outcomes of interest being compliance and recidivism. Outcomes were assessed with time-to-event recidivism data and frailty modeling was used to account for the clustering of parole agents within districts. Findings indicate that GPS monitoring is more effective than traditional supervision. A pattern of divergence in outcomes was observed during the study period. The GPS group demonstrated significantly better outcomes. For the control group: 1) the compliance hazard ratio of a sex-related violation was nearly three times as great and 2) the recidivism hazard ratio for any arrest was more than twice as high. Similarly, for both a parole revocation and any return-to-custody event, the hazard ratio suggests that these events are about 38 percent higher among the subjects who received traditional parole supervision. The cost analysis indicated that the GPS program costs roughly $8.51 more per day per parolee than traditional supervision. The process evaluation revealed that the GPS program was implemented with a high degree of fidelity across the dimensions examined: adherence, exposure, quality of program delivery, and program differentiation.