Background. Neurodegenerative diseases (ND) as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis represent a growing cause of disability in the developed countries. The underlying physiopathology is still unclear. Several lines of evidence suggest a role for oxidative stress and NADPH oxidase 2 (NOX2) in the neuropathological pathways that lead to ND. Furthermore, recent studies hypothesized a role for gut microbiota in the neuroinflammation; in particular, lipopolysaccharide (LPS) derived from Gram-negative bacteria in the gut is believed to play a role in causing ND by increase of oxidative stress and inflammation. The aim of this study was to assess NOX2 activity as well as serum 8-iso-prostaglandin F2α (8-iso-PGF2α), serum H₂O₂, and LPS in patients with ND compared to controls. Methods. One hundred and twenty-eight consecutive subjects, including 64 ND patients and 64 controls (CT) matched for age and gender, were recruited. A cross-sectional study was performed to compare serum activity of soluble NOX2-dp (sNOX2-dp), blood levels of isoprostanes, serum H₂O₂, and LPS in these two groups. Serum zonulin was used to assess gut permeability. Results. Compared with CT, ND patients had higher values of sNOX2-dp, 8-iso-PGF2α, H₂O₂, and LPS. Simple linear regression analysis showed that sNOX2-dp was significantly correlated with serum LPS (Rs=0.441; p<0.001), zonulin (Rs=0.411; p<0.001), serum H₂O₂ (Rs=0.329; p<0.001), and 8-iso-PGF2α (Rs=0.244; p=0.006). LPS significantly correlated with serum zonulin (Rs=0.818; p<0.001) and 8-iso-PGF2α (Rs=0.280; p=0.001). A multiple linear regression analysis was performed to define the independent predictors of sNOX2-dp. LPS (SE, 0.165; standardized coefficient β, 0.459; p<0.001) and 8-iso-PGF2α (SE, 0.018; standardized coefficient β, 0.220; p=0.005) emerged as the only independent predictive variables associated with sNOX2-dp (R2=57%). Conclusion. This study provides the first report attesting that patients with ND have high NOX2 activation that could be potentially implicated in the process of neuroinflammation.