However, when evaluated longitudinally, CR had either no effect on, or a negative association with, cognitive outcomes. Regardless of the CNS disease of the individuals, almost all of the studies reported a positive association between CR and cognitive outcomes when they were evaluated cross-sectionally. Education level was the most commonly used measure for CR, and various neuropsychological tests were used to measure cognitive outcomes. Seventeen studies met the predetermined inclusion criteria and were selected for review. We performed a systematic search of PubMed, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and PsychInfo using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The purpose of our paper is to systematically review the effects of CR on cognitive outcomes in individuals with neurodegenerative and structural CNS diseases. Cognitive reserve (CR) has been proposed to account for functional outcome differences in brain pathology and its clinical manifestations.