The paper concludes that the benefits of incrementally processing greater numbers of serious juvenile offenders in adult criminal courts may exceed the costs if it leads to more certain and longer incapacitation of those juveniles most likely to commit dangerous and expensive crimes. Such benefits would be undermined, however, if the costs of implementing such a policy outweighed the benefit of more and longer incapacitation. One such cost might be "net-widening," which would involve bringing more relatively minor juvenile offenders into the adult system and increase their numbers in prisons. Also, if the increasing number of juveniles being processed in the adult system were to reduce the quality of processing adult offenders, then the cost of the adult processing of juveniles could exceed the benefits to the community. The costs would be greatest if the transferred juveniles imprisoned posed less risk to the community than adult offenders diverted to supervision in the community. Crime costs for the community are greatest when offenders commit violent crimes, expensive property crimes, or a large number of crimes. Any jurisdictional change in the processing of juveniles will only yield a net benefit if this leads to more incapacitation or effective rehabilitation of offenders most likely to commit such crimes. This will happen only if the extra costs of arresting, trying, and treating or sentencing such offenders are less than the savings achieved from reducing the severity and number of crimes they commit. This paper describes a cost-benefit methodology for making these estimations. 1 figure and 45 references