Background/Aim: Although clinical and immunological findings in steroid-sensitive nephrotic syndrome (SSNS) favor an immunopathogenesis, many issues remain unsolved. Comprehensive studies analyzing cellular and humoral immunity in SSNS are scarce, and few studies addressed the effect of steroids on immunological factors. Methods: We therefore performed a cross-sectional study of T and B lymphocyte populations in 89 children during the different stages of the disease and related the findings to parameters of humoral immunity and treatment with steroids. Results: In untreated relapse, an increase in the proportion of activated CD3+ lymphocytes with a concomitant reduction of CD19+ B cells was noted compared to healthy controls. Conversely, patients with steroid dependency, relapsing on alternate-day steroids, showed a decline of the absolute numbers as well as proportion of CD4+ lymphocytes but a relative increase in CD19+ B cells, compared to healthy controls. Also untreated remission was characterized by an absolute and relative decrease in CD4+ lymphocytes compared to healthy controls which was accompanied by a significant increase in the proportion of CD8+ and also activated CD3+ lymphocytes. Steroid-induced remission resulted in suppression of absolute and relative CD4+, while absolute and relative B cells were upregulated in this group compared to untreated remission. Summary and Conclusion: Alterations of lymphocyte populations in SSNS are not limited to relapse but seem to be more pronounced in remission and show a different profile with steroid treatment. Changes of lymphocyte populations do not only affect T but also B lymphocytes, which may be of relevance in the pathogenesis of this disorder.