This article concludes that a thorough forensic evaluation of the intellectual and adaptive functioning of a defendant must be conducted in the course of the court’s deciding whether a defendant is “mentally retarded” for the purpose of eligibility for the death penalty under the provisions of State law. This precludes setting a specific IQ score as the sole measure of mental retardation. In arguing that the trier of fact must be given more information than is necessary for making a clinical diagnosis of mental retardation, the article cites the case of People v. Vidal (2004) in California. The prosecution filed the case as a capital offense, and the defense responded by filing a motion to preclude the imposition of the death penalty under “Atkins,” as implemented in California law. Across the administration of several relevant tests, Vidal consistently scored in the mentally retarded range in terms of his Verbal Intelligence Quotient (VIQ), while his Performance Intelligence Quotient (PIQ) ranged from average to high average. Vidal’s full Scale Intelligence Quotient (FSIQ) ranged from borderline mental retardation to average intelligence. With each test administration, there was a significant split between his VIQ and PIQ. The trial judge ruled that Vidal’s VIQ, combined with deficits in adaptive functioning, was sufficient to establish his incapacity for “premeditation, deliberation, appreciation of concepts of wrongful conduct, ability to think and weigh reasons for and not for doing things, and logic and foresight.” 14 references