Previous research has supported the use of percent retention scores in the neuropsychological assessment of memory, and many widely used memory measures provide for the calculation and normative comparison of these scores. The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), an increasingly utilized assessment tool for cognitive impairment, provides normative data on delayed memory total raw scores only. The current study was aimed at determining the diagnostic accuracy of a novel percent retention score calculated from RBANS verbal memory subtests (delayed recall minus last learning trial) when distinguishing between normal controls, individuals diagnosed with Mild Cognitive Impairment, and individuals diagnosed with Alzheimer's disease. Results revealed excellent diagnostic accuracy of the RBANS percent retention scores when discriminating between the three groups. Findings suggest that RBANS percent retention scores provide excellent diagnostic accuracy offering supplementary information to clinicians and researchers alike.