Recent studies have provided evidence that uric acid (UA), a natural antioxidant, may play a role in the development and progression of Parkinson's disease (PD) and of dementia. In this clinical study we were therefore interested in the role of UA in Lewy body disorders (LBD), which includes Parkinson's disease (PD) and a common form of neurodegenerative dementias, dementia with Lewy bodies (DLB). Ninety-five LBD patients (55 non-demented PD patients, PDND; 20 PD patients with dementia, PDD; and 20 DLB patients) and 76 controls underwent clinical and biochemical analyses including, from a subcohort, cerebrospinal fluid (CSF) analyses, and analysis of three single nucleotide polymorphisms (SNPs) known to be associated with altered serum UA levels. We confirmed previous findings of lowered serum UA levels in LBD patients compared to controls. In CSF, UA levels were significantly higher in PDND patients (median 0.7 mg/dl) compared only to demented LBD patients (0.4 mg/dl; p = 0.03), but not to controls (0.5 mg/dl; p = 0.12). CSF UA levels correlated positively with CSF Aβ42 levels. This correlation was highest in controls (ρ = 0.67), intermediate in PDND (ρ = 0.49), but not observable in demented LBD patients (ρ = 0.10). These findings suggest an involvement of serum UA in LBD occurrence, and an involvement of CSF UA in cognitive decline in LBD, possibly through the Aβ pathway. SNP rs1165205 (SLC17A3) was weakly associated with altered CSF UA levels. Taken together, our results provide first evidence for disease-relevant but potentially distinct roles of UA in the blood and CSF compartment, respectively, in LBD.