Objective: Cognitive deficits can occur even in the early stages of Parkinson's disease (PD) and are often subtle, but discernible with neuropsychological testing, and are progressive. Rasagiline, an MAO-B inhibitor, has recently shown benefits consistent with a possible disease modifying effect. We hypothesized that rasagiline would slow the decline of cognition in non-demented patients with mild to moderate PD. Method: 50 participants recruited from a Movement Disorders Clinic with mild to moderate PD, Mini Mental Status (MMSE) scores greater than 23/30, and without depression participated in a 6 month, double blind, placebo controlled trial with rasagiline. Participants were not randomized on other PD medication use and PD medication use remained stable over the course of the trial. Participants completed a battery of neuropsychological tests assessing a range of cognitive domains both at baseline and after 6 months of receiving 1 mg of rasagiline or placebo daily. 23 rasagiline and 22 control participants completed the study. Results: Independent t-tests found our two groups to be equivalent in age, motor impairment, gender, PD medication status, and MMSE score. Repeated measures ANOVA comparing pre- and post-treatment scores on tests of attention, executive functioning, visuospatial and language abilities, and memory failed to find significant differences between the rasagiline and control groups. Conclusion(s): Use of rasagiline was not found to positively impact cognitive functioning in this study of non-demented, mild to moderate stage PD patients. Future research may exam the potential effects of rasagiline on cognition over a greater period of time and could involve individuals with demonstrable mild cognitive impairments.