Abstract Background: Type 1 diabetes (T1D) results from T-cell-mediated autoimmune destruction of the insulin-producing pancreatic islet Beta cells. This breakdown of immunological self-tolerance results in auto reactivity to islet self-antigens. This requires genetic susceptibility as well as environmental factors (gene environmental interaction). It is believed that numerical and functional balance between killer cells (CD4+ and CD8+) and regulatory T-cells in the pancreatic infiltrate determines the extent of Beta cell destruction. Aim of Study: To study the number and function of Treg CD4+ CD25+ T-cells in infants and children with recent onset type 1 diabetes and to compare the results with the Treg CD4+ CD25+ T-cells in the siblings of the diabetic child and control subjects. Patients and Methods: This study was performed on60 patients meeting the diagnostic criteria of type I diabetes, together with 20 children of their non diabetic siblings were recruited at the Diabetes Endocrine and Metabolism Pediatric Unit (DEMPU) at Cairo University Children's Hospital in the period from December 2011 to October 2012. In addition to 20 children with age and sex-matched, none of whom had either a personal or family history of diabetes or other autoim-mune pathologies as control were included in the study. Results: Show no statistically significant relation of CD4 CD25 T-lymphocytes to age, anthropometric measures (weight & height), laboratory data including HBA1C, lipid profile or thyroid function tests, the insulin dose and the severity of the case presentation (whether classic onset or DKA). Also there was no statistically significant difference between the 3 groups (diabetic – non diabetic siblings – controls) regarding CD4CD25 T- lymphocytes levels by the one-way ANOVA test. Conclusion: The sensitivity of CD4 CD25 T-lymphocytes in case of type 1 diabetes was 60% and the specificity was 47%. The PPV (positive predictive value) and the NPV (neg-ative predictive value) were 55% and 67% respectively. Such results conclude that CD4 CD25 T-lymphocytes cannot be taken as a valid marker in case of type I diabetes.