Dysfunctional T-lymphocyte immunity plays an important role in the pathophysiology of immune thrombocytopenic purpura (ITP). Cytotoxic T-lymphocyte antigen 4 (CTLA-4)—a surface marker expressed on T regulatory cells and activated T lymphocytes—is a negative modulator of T-cell responses. Polymorphisms of the CTLA-4 may alter the level of antigen expression and hence may influence immune regulation. The study aimed to evaluate the possible contribution of CTLA-4 exon 1 49 A>G polymorphism to the pathogenesis of ITP and its relation to age of disease onset, clinical course, and response to therapy. Genotyping of CTLA-4 exon 1 49 A>G was performed in 100 pediatric patients with ITP and 259 healthy individuals by polymerase chain reaction-restricted fragment length polymorphism. No significant differences existed in genotype or allele distributions between patients and controls for the studied polymorphism. Comparable genotypes and allele frequencies were obtained between the 2 groups after their stratification by age of disease onset, clinical course, or response to therapy. In conclusion, CTLA-4 exon 1 49 A>G polymorphism is not associated with susceptibility to ITP in the Egyptian population; neither it affects the clinical picture of the disease.