Background: Immunological tolerance is compromised in children with Immunological Thrombocytopenic Purpura (ITP), an autoimmune disease. The purpose of this study was to measure the levels of lymphocyte subsets in children with ITP and assess how these subsets related to the patients' chronic illness and responsiveness to treatment. Techniques: The pediatric hematology outpatient clinic at Zagazig University Hospitals served as the site of this case-control study. Sixty-four patients (16 with newly diagnosed ITP, 16 with persistent ITP, 16 with chronic ITP, and 16 healthy children as a control group) participated in the study. Using flowcytometry, all of the study's patients and controls had their lymphocyte subsets evaluated. Results: CD3+, CD4+ and CD56+ lymphocytes were significantly lower in patients with ITP compared to controls while CD8+ and CD19+ lymphocytes were significantly higher in patients with ITP compared to controls. Apart from CD8+ lymphocytes which were significantly higher in patients with chronic ITP compared to other patients' groups, there was no significant difference among different patients' groups in relation to different lymphocyte subsets. Patients with newly diagnosed ITP who responded to 1st line therapy had lower CD4+ and higher CD8+ and CD19+ lymphocytes compared to those who did not respond to 1st line therapy. Conclusion: We concluded that lymphocyte subsets play a significant role in the pathogenesis, chronicity and response to treatment in childhood ITP.