Background: Vitamin D has shown an immune-modulatory effect in different studies. Vitamin D stimulates Tregs and inhibits Th17 cells. The immune-modulatory role of vitamin D in chronic kidney disease (CKD)) and renal transplant patients is unclear. We measured whether different serum levels of vitamin D were associated with an increased or decreased presence of lymphocyte subsets including Treg and Th17 cells in end-stage renal disease (ESRD) and renal transplant recipients. Methods: Eighty-seven renal transplant recipients and 53 end-stage renal disease (ESRD) patients were enrolled in this study. The absolute counts of CD4 + and CD8 + T, CD16 + CD56 + NK, CD19 + B, CD4 + CD25 + CD127- Foxp3 + (Tregs), Helios + Tregs, CD38 + Tregs, and CD4 + CD17 + (Th17) cells were analyzed in peripheral blood in both patient groups. In addition, serum 25 (OH) D-3, 1, 25 (OH)(2) D-3, IL-6, IL-17, IL-23, and TGF-beta(1) were measured. The association between lymphocyte subset counts and 1, 25 (OH)(2) D-3 or 25 (OH) D-3 was studied, as was the association between serum IL-6, IL-17, IL-23, or TGF-beta(1) and 1,25 (OH)(2) D-3 or 25 (OH) D-3. Results: Serum 25 (OH) D-3 and 1,25 (OH)(2) D-3 levels were not independently associated with peripheral CD4 + T, CD19 + B, CD16 + CD56 + NK, Treg, or Th17 cell counts. In contrast to serum 25 (OH) D-3, serum1, 25 (OH)(2) D-3 was positively associated with CD8 + T cells counts in renal transplant recipients. Conclusion Our findings indicate low utility of serum 25 (OH) D-3 and 1, 25 (OH)(2) D-3 levels in predicting a change in lymphocyte subset counts in ESRD and renal transplant patients.