Abstract Background: X-linked agammaglobulinemia type 1 or XLA is one of the most common pediatric inborn errors of immunity affecting the humoral immune system. The condition is caused by a mutation in the Bruton tyrosine kinase gene (BTK), located in the long arm of the X-chromosome. BTK is crucial for B lymphocyte differentiation and activation. Therefore, a defect in BTK results in B lymphocytes maturation arrest, absence of plasma cells, and failure of immunoglobulins (Igs) production. XLA affected individuals present with a history of frequent sever pyogenic infections such as pneumonia, conjunctivitis, otitis media, and bacteremia. Laboratory evaluation classically reveals undetectable Igs and the absence of B-cells. The mainstay treatment is immunoglobulins replacement which can be administered intravenously (IVIG) or subcutaneously (SCIG). In addition to, aggressive antimicrobial treatment to reduce complications such as bronchiectasis or invasive bacterial infections during active infections. Aim: To report the clinical presentation, immune features, and genetic mutation in one case of a four-year-old boy with a novel mutation in the BTK gene leading to XLA. Results: The Patient’s chart was reviewed. We describe the phenotypical and diagnostic characteristics of an established case in a four-year-old boy who suffered from recurrent infections. The genetic reading report revealed a pathogenic novel mutation in the BTK gene (c.1953C>A: p Tyr651*), and the flow-cytometry result of 0% C19+ (B-cells), and low Is serum levels. Discussion: We report the clinical presentation, immune features, and genetic mutation in a patient with novel mutations in the BTK gene causing XLA. Genetic analysis along with patient history and physical examination and laboratory results are necessary to identify and diagnose XLA with pathogenic mutation in the BTK gene.