Objectives The present study was undertaken to evaluate the cognitive profile of Parkinson's disease (PD) patients with REM sleep behavior disorder (RBD) and to correlate with the clinical stage and polysomnographic variables. Methods The study included 25 PD patients who had RBD and 25 PD patients who based on two questionnaires were determined as not having RBD. These patients underwent overnight polysomnography (PSG) and neuropsychological assessment using a defined battery of tests. Results The mean age of the patients with clinically probable RBD (RBD+) was 60.4 ± 8.2 years and PD patients without RBD (RBD-) was 57.3 ± 6.6 years (p = 0.14). The mean age at onset of the disease was 53.7 ± 9.4 years for RBD+ and 49.8 ± 7.8 years for RBD-patients (p = 0.12). The mean Unified Parkinson Disease Rating Scale (UPDRS) part III OFF score was 27.4 ± 11.1 for RBD+ and 32.7 ± 8.2 for RBD- (p = 0.06). The total sleep time of the patients was 4.3 ± 1.7 h with sleep efficiency of 53.8 ± 21.0%. Patients with RBD+ were found to have significant impairment in many neuropsychological tests compared to RBD-. Conclusions RBD + patients had significant impairment in MMSE, category fluency test (FAS test), frontal assessment battery, attention (digit span backwards, Corsi span), verbal memory (story recall) and Rey's auditory verbal learning test. These patients also had poor sleep quality.