The proteoglycan NG2 plays a major role in proliferation, migration, and differentiation of pericytes and NG2 cells in the brain. We have previously reported decreased soluble NG2 (sNG2) levels in cerebrospinal fluid (CSF) from patients with Alzheimer's disease (AD) and a relationship between sNG2 and AD biomarkers in these patients. To further investigate whether alterations in sNG2 is specific to AD pathology, we measured levels of sNG2 in CSF from a patient cohort consisting of non-demented controls (n = 51), patients with Parkinson's disease (PD) (n = 61), and patients with dementia with Lewy bodies (DLB) (n = 37), two synucleinopathies whereof the latter disorder frequently coincides with amyloid-β pathology similar to AD. We found decreased sNG2 concentrations in DLB patients, but not in PD patients, compared to controls. Levels of sNG2 in controls and PD patients correlated to T-tau, P-tau, α-synuclein, and neurosin. Only one correlation, between sNG2 and neurosin, was found in DLB patients. Analysis of a second cohort consisting of controls (n = 23) and DLB patients (n = 31) showed that the result was reproducible, as lower levels of sNG2 again were found in DLB patients compared to controls. We conclude that lower levels of sNG2 levels indicate a DLB-related impact on NG2 expressing cells foremost associated with neuropathology linked to accumulation of amyloid-β and not α-synuclein.