The prevalence of serious mental illnesses in jail populations is significantly greater than in the general population. Identifying individuals who warrant psychiatric evaluations is important and benefits correctional staff as well as detainees. One widely used screening instrument intended for this task is the Referral Decision Scale (RDS). This paper reviews the development and validation of the RDS. Using data from a multisite study which assessed postrelease outcomes for detainees with mental illness, various types of validity are addressed. The results confirm that the RDS has some inherent characteristics that seriously limit its practical application as a screening instrument for use by correctional staff.