The prevalence of serious mental illness in jail populations is significantly greater than in the general population. Identifying individuals who warrant psychiatric evaluation 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). To review various types of validity of the RDS, this paper used data from a multisite study which assessed postrelease outcomes for detainees with mental illness. Results confirmed that the RDS has some inherent characteristics that seriously limit its practical application as a screening instrument for use by correctional staff: the ability of the RDS to screen for persons who may need treatment and the content validity of the root questions and construct validity of items based on lifetime instead of current status. Tables, appendix, references