Immune thrombocytopenic purpura (ITP) is an autoimmune syndrome involving platelets destruction and suppression of platelet production that may predispose to bleeding. Protein tyrosine phosphatase non-receptor 22 gene (PTPN22) is an important negative regulator of signal transduction through the T-cell receptors (TCR). A single nucleotide polymorphism (SNP) 1858C > T within this gene was reported to be associated with increased risk of autoimmune diseases. The aim of the work was to study the frequency of the 1858C > T single nucleotide polymorphism in the PTPN22 gene in Egyptian ITP patients. After full clinical and laboratory examination of our subjects, the expression of the PTPN22 (1858C > T) gene polymorphism was analyzed in 60 ITP patients—40 childhood ITP (26 acute and 14 chronic) and 20 adulthood ITP (eight acute and 12 chronic)—and 100 healthy controls using a polymerase chain reaction-restriction fragment length polymorphism assay [PCR-RFLP]. The PTPN22 1858C > T SNP was significantly overrepresented in ITP patients than controls. It was detected in 11 childhood ITP (27.5%) and five adulthood ITP (25.0%) compared to 8.0% in controls (p = 0.002, p = 0.02) when comparing childhood ITP and adulthood ITP to controls, respectively. The T allele was significantly higher in ITP patients than controls. It was 20% for childhood ITP, 15% in adulthood ITP and 4% in controls (p = 0.002, p = 0.05) when comparing childhood ITP and adulthood ITP to controls, respectively. From this study we concluded that the PTPN22 1858C > T polymorphism is more prevalent in ITP patients; thus, it may be considered as a genetic risk factor in development of ITP in Egyptian patients.