OBJECTIVE: To evaluate whether aerobic exercise improves cognition in adults diagnosed with neurologic disorders. DATA SOURCES: The Cochrane Central Register of Controlled Clinical Trials, MEDLINE, CINAHL, PubMed, EMBASE, PEDro, AMED, SPORTDiscus, PsycINFO, ERIC, and Google Scholar, with the last search performed in December 2010. STUDY SELECTION: We included controlled clinical trials and randomized controlled trials with adults diagnosed with a neurologic disorder. Studies were included if they compared a control group with a group involved in an aerobic exercise program to improve cardiorespiratory fitness and if they measured cognition as an outcome. DATA EXTRACTION: Two reviewers independently extracted data and methodologic quality of the included trials. DATA SYNTHESIS: From the 67 trials reviewed, a total of 7 trials, involving 249 participants, were included. Two trials compared the effectiveness of yoga and aerobic exercise in adults with multiple sclerosis. Two trials evaluated the effect of exercise on patients with dementia, and 2 trials evaluated the effectiveness of exercise to improve cognition after traumatic brain injury. One trial studied the effect of a cycling program in people with chronic stroke. Lack of commonality between measures of cognition limited meta-analyses. Results from individual studies show that aerobic exercise improved cognition in people with dementia, improved attention and cognitive flexibility in patients with traumatic brain injury, improved choice reaction time in people with multiple sclerosis, and enhanced motor learning in people with chronic stroke. CONCLUSIONS: There is limited evidence to support the use of aerobic exercise to improve cognition in adults with neurologic disorders. Of the 67 studies retrieved, less than half included cognition as an outcome, and few studies continued the aerobic exercise program long enough to be considered effective. Further studies investigating the effect of aerobic exercise interventions on cognition in people with neurologic conditions are required.