Background: The 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) C1858T within this gene was shown to be a risk factor for several autoimmune diseases.Objectives: The aim of this study was to analyze a possible association between C1858T SNP of protein tyrosine phosphatase non receptor type 22 (PTPN22) and T1DM.Subjects and Methods: The current study evaluated the PTPN22 C1858T polymorphism in 50 previously diagnosed T1DM subjects and 30 healthy age and sex matched subjects with no family history of T1DM or any other types of autoimmune disease. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism, HbA1c is determined at the time of the study. Results: Statistical comparisons for the distribution of genotypes and allele frequency for the PTPN22 C1858T polymorphism between T1DM patients and controls showed no statistically significant difference. There was a statistically non-significant association between the PTPN22 genotypes and HbA1c, body mass index, and age at onset of T1DM among the patients' group where the P values were: 0.951, 0.11 and 0.801 respectively. Conclusion: No statistically significant association was found between the PTPN22 C1858T polymorphism and T1DM.