bjective: 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. Design and method: 63 ESKD patients (textgreater18 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 vs 1.60 ± 1.82 micromol/l, in HD and PD, respectively, p = 0.841), as well as the duration needed for task completion (191.53 ± 124.27 vs 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 vs 1.49 ± 0.95 micromol/l, respectively, p = 0.262). In the total cohort, the average response in brain oxygenation during handgrip exercise was inversely correlated with dialysis vintage (p textless 0.05). Conclusions: 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.