Cognitive dysfunction is common in Parkinson's disease (PD). Low plasma uric acid level is a risk factor for PD but its association with cognitive impairment in PD has not been previously studied. In the present Study urine uric acid level as well as plasma uric acid- and homocysteine levels were measured in 40 patients with PD. Comprehensive neuropsychological tests including computerized tasks were performed on all. Both low plasma and low urine uric acid levels associated with decreased neuropsychological performance. In Multiple linear regression low urine Uric acid level predicted worse performance in the Picture completion subtest of the Wechsler Adult Intelligence Scale-Revised (WAIS-R) (p = 0.003) and in the Rule shift cards test of the Behavioral Assessment of the Dysexecutive Syndrome (BADS) (p = 0.04). Low plasma uric acid level predicted worse performance both in the Picture completion (p = 0.02) and Similarities subtest of the WAIS-R (p = 0.02). Reaction time and the tune spent on cognitive processing in the Statement verification task were inversely correlated with the Uric acid levels (p = 0.0001). There was no correlation between the homocysteine level and neuropsychological performance. Instead, the plasma Uric acid and homocysteine levels correlated significantly and their possible association in PD is discussed, (c) 2008 Elsevier Ltd. All rights reserved.