The United States Supreme Court has long held that the death penalty cannot be imposed arbitrarily, and that during sentencing in capital cases, jurors must be provided with guidelines to assist them in narrowing down the class of individuals for whom the death penalty is appropriate. Typically, this is accomplished through the presentation of aggravating and mitigating evidence. One aggravating factor is a capital offender’s future dangerousness, or the likelihood that the individual will engage in violent institutional misconduct while in prison. Future dangerousness may be assessed using a variety of measures; Hare’s Psychopathy Checklist-Revised (PCL-R), a measure of personality traits associated with psychopathy, is one such measure that informs future dangerousness testimony. However, research suggests that the predictive validity of the PCL-R regarding violent institutional misconduct is weak-to-moderate, and that presentation of such evidence can prejudice jurors such that they will be more likely to assign the death penalty than they would in the absence of such evidence. These findings are concerning, particularly considering the severe social costs and individual rights deprivations associated with the death penalty. This Article will trace the history of Supreme Court capital sentencing decisions, examine the scientific literature regarding the predictive validity and bias potential for PCL-R evidence in capital sentencing, and argue that, in light of this weak literature base and the deleterious impact that misguided capital sentencing can have, applying the Federal Rules of Evidence to capital sentencing contexts may present an effective solution for keeping specious future dangerousness evidence out of the courtroom.