Backgroundː Chronic kidney disease stage G5 (CKD G5) patients show an activated but impaired immune system. One function of the FOXP3+ regulatory T (Treg) cells is to preserve tolerance to self while maintaining the ability to fight infectious agents. The aim of this pilot study is to evaluate longitudinal changes in Treg cells before and 1 month after the first dialysis treatment. Materials and methodsː CKD G5 patients not yet on dialysis were enrolled and started on hemodialysis (HD) or peritoneal dialysis (PD). Tregs were analyzed by flow cytometry at two time points: T0 (before the first dialysis treatment) and T1 (1 month after the first dialysis session). Wilcoxon test for dependent samples was used to compare the mean percentage difference between T0 and T1: Δ% = 100 × [(T1 - T0) / T0]. Resultsː 21 patients were enrolled: 8 on HD and 13 on PD. The proportion of total lymphocytes (low side scatter lymphocyte gate) and T lymphocytes (in the CD3+CD4+ gate) did not change significantly 1 month after the start of dialysis in both groups. Treg cells (as CD25+FOXP3+, FOXP3+, or CD25+CD127-), analyzed as percentage of the lymphocyte gate, showed a significant increase post PD (CD25+FOXP3+: median = 35.92; p = 0.0425; FOXP3+: median = 30.85; p = 0.0479 and CD25+CD127-: median = 23.71; p = 0.0215). The same populations, did not change 1 month after the first dialysis session. Conclusionː Our study is the first to evaluate longitudinal effects of dialysis on Treg cells in uremia and suggests that PD was more effective in increasing Treg levels 1 month post initiation of dialysis and may contribute to improvement of inflammatory status. Thus, PD may contribute to better outcomes for patients with renal dysfunction, also maintaining homeostasis of peritoneal and renal tissues.