Background: The protein tyrosine phosphatase nonreceptor 22 gene (PTPN22) is an important negative regulator of signal transduction through the T-cell receptors (TCR). Recently a single-nucleotide polymorphism (SNP) 1858 C/T within this gene was shown to be a risk factor for several autoimmune diseases, such as rheumatoid arthritis (RA), Graves’ Disease (GD), systemic lupus erythematosus (SLE), Wegener's granulomatosis (WG) and type 1 diabetes mellitus (T1D). Aim of this study: To analyze a possible association between 1858 C/T SNP and T1D in Egyptian population. Patients with T1D and healthy controls were genotyped for the 1858 C/T SNP in PTPN22 gene. Results: 17% of T1DM patients were TT/CT compared to 0% of controls. This difference is highly significant (P=0.002) and odds ratio (95% confidence interval) was 1.602(1.404-1.828). Also, 181alleles of T1DM patients were C (90.5%) compared to 100 alleles (100%) of controls with P value = 0.001, this difference is highly significant. Conclusion: The current study supports the significant association between PTPN22 1858 C/T SNP and T1D. 1858T/T genotype was observed more frequently in T1D patients compared to control subjects.