BACKGROUND: ITP is an immune-mediated disorder showing increased platelet destruction and reduced platelet production. Glucocorticoids are the first-line treatment, but 10-20% of patients are insensitive to them. We should avoid the irrational use of steroids for treating ITP. No markers exist to predict treatment responses in ITP. Recently, a few studies showed abnormal ratio and function of Tregs in ITP patients and that the levels of Tregs change after glucocorticoid treatment. We aimed to study the value of CD8+ CD25+ Tregs in predicting glucocorticoid sensitivity in newly diagnosed ITP patients. RESEARCH DESIGN AND METHODS: This cohort (longitudinal) study included 60 ITP patients. The baseline platelet counts and levels of CD8+ CD25+ Tregs were measured at diagnosis. The response to steroids was evaluated after 2 weeks of treatment, then after 3 months and 6 months. RESULTS: The ROC curve was plotted, and the CONCLUSIONS: This study couldn't confirm the value of CD8+CD25+ Tregs in predicting glucocorticoid sensitivity in ITP, but there was a significant positive correlation between the CD8+CD25+ Tregs percentage and the steroids' response after 2 weeks. Therefore, further studies are recommended.