Background: Selective Immunoglobulin A deficiency (SIgAD) is known to be one of the most frequent primary immunodeficiency diseases. Several studies worldwide confirm the increased frequency of this disease among type 1 diabetes mellitus (T1DM), yet this has not been studied in Egypt. Objective: This work aimed to define the prevalence of SIgAD among Egyptian patients with T1DM. Patients and Methods: Fifty patients with T1DM were compared to fifty apparently healthy individuals. Serum levels of IgA, IgG, and Immunoglobulin M (IgM) levels were measured by Nephelometry to all participants. Results: The mean age of the diabetic group was 24.5 ± 5.3 years. Thirty out of fifty patients with T1DM (60%) were diagnosed as SIgAD with, female predominance (66.7% of SIgAD). We also found a significant relationship between SIgAD and diabetic ketoacidosis (P-value<0.001). Serum IgA levels were positively correlated to IgG and IgM. Conclusion: The current study displays 60% prevalence of SIgAD among adult Egyptians with T1DM, which is higher than stated in other countries.