Abstract BACKGROUND AND AIMS Cognitive impairment is highly prevalent in end-stage kidney disease (ESKD) individuals. Brain oxygenation is a parameter that plays major role in cognitive function. This study aimed to examine for the first time changes in brain oxygenation during a mental and a mild physical task in hemodialysis (HD) and peritoneal dialysis (PD) patients. METHOD A total of 63 ESKD patients (≥18 years old) were enrolled in this cross-sectional study. Patients were allocated in two groups according to dialysis modality (n = 29 HD and n = 34 PD). All participants underwent a mental (countdown from 100 to 0 by 7, performed twice) and a mild physical task (a 3-min intermittent handgrip exercise at 35% of maximal handgrip strength). Changes in brain oxygenation [oxy—(O2Hb), deoxy—(HHb) and total—(tHb) hemoglobin] during the two tasks were continuously recorded via near-infrared spectroscopy (NIRS, Artinis). RESULTS Age, sex and dialysis vintage did not differ between the two groups. The average response in brain oxygenation during the mental task (O2Hb change from rest: 1.51 ± 1.68 versus 1.60 ± 1.82 μmol, in HD and PD, respectively, P = 0.841), as well as the duration needed for task completion (191.53 ± 124.27 versus 200.19 ± 118.84 s, P = 0.781) were similar between groups. Furthermore, the average response in brain oxygenation during the handgrip exercise also did not differ between the groups (O2Hb change 1.20 ± 1.03 versus 1.49 ± 0.95 μmol, respectively, P = 0.262). In the total cohort, the average response in brain oxygenation during handgrip exercise was inversely correlated with dialysis vintage (P < 0.05). CONCLUSION Dialysis modality does not appear to have an impact on brain oxygenation, as HD and PD patients presented similar responses during a mental and a mild physical task. Dialysis vintage may negatively affect brain oxygenation in ESKD individuals.