BACKGROUND Primary immunodeficiency disorders (PID) are a group of hereditary disorders characterized by an increased susceptibility to severe and recurrent infections, autoimmunity, lymphoproliferative disorders, and malignancy. OBJECTIVE To evaluate the demographic and clinical data of PID patients diagnosed in a referral pediatric hospital. METHODS All PID cases with a confirmed diagnosis, according to the criteria of International Union of Immunological Societies, who were referred to the Children's Medical Center in Tehran, Iran, between March 2006 and March 2013 were enrolled in this retrospective cohort study. RESULTS Three-hundred and seven PID patients were investigated. Predominantly antibody deficiencies were the most common group of PID observed in 118 cases (38.4%), followed by the well-defined syndromes with immunodeficiency in 52 (16.9%), congenital defects of phagocyte in 45 (14.7%), combined immunodeficiencies in 36 (11.7%), autoinflammatory disorders in 34 (11.4%), immune dysregulation in 11 (3.6%), complement deficiencies in 7 (2.3%), and defects in innate immunity in 3 (1%). Selective IgA deficiency was the most prevalent disorder which affected 46 individuals (14.9%). The median diagnostic delay was 15 months. CONCLUSIONS Increased awareness and availability of diagnostic tests could result in the better recognition of more undiagnosed PID cases and a decrease in diagnostic delay.