This report provides an estimate of the annual cost savings to the Western Australian Government of proactively diverting young offenders from the court system and from detention in remand in accordance with the Young Offenders Act 1994 (YO Act 1994). The cost impact of four pre-sentencing juvenile justice system redirection measures is examined in the study. These measures are: police cautions; referrals to juvenile justice teams by the police; referrals to juvenile justice teams by the Children’s Court; and, court conferences. On a full cost basis, the total cost reduction realised by using redirection as opposed to the pre-YO Act practices is estimated to be $8.7 million per annum or 10.5 per cent of Juvenile Justice System costs. The report is divided into three sections. Section one outlines the key features of the juvenile justice system as it presently operates and of the operation of the juvenile justice system immediately prior to the introduction of the YO Act 1994. Section two sets out the method for undertaking the cost benefit analysis while section three details the results. It provides a detailed breakdown of juvenile justice system costs by both juvenile justice system contact type and by department/agency. Juvenile justice system costs are also presented at different levels of cost aggregation (salaries and on-costs through to all recurrent costs and finally full costs incorporating fixed costs). This appears to be the first time juvenile justice system costs have been estimated across departments/agencies and through the full sequence of juvenile justice system contacts. As such, the study’s results have benefits beyond the cost benefit analysis itself and should prove a valuable resource for government departments and agencies providing juvenile justice system services.