Purpose: X-linked agammaglobulinemia (XLA) is a primary immunodeficiency caused by mutations in the Bruton’s tyrosine kinase (Btk) gene. The aim of this study is to investigate the clinical manifestations, molecular features and treatment status of XLA in Korean patients at Seoul National University Children’s Hospital. Method: Fourteen Korean boys with XLA showing serum agammaglobulinemia, non-detectable to less than 2 % peripheral B cells, and mutation on Btk gene were enrolled. We observed the clinical features, laboratory findings, status of treatment and complications of XLA patients Result: All XLA patients had a history of recurrent bacterial infections before diagnosis and 20% of them had a neutropenia. Among these, 35.7% of XLA patients had a family history and 75% of their mothers were carriers. Btk gene study showed variable gene mutations in Xq22 including 9 Amino acid substitution, 3 frameshift, 1 premature stop codon, 1 splice defect. After IVIG replacement therapy, infection episodes decreased but complications such as bronchiectasia and chronic sinusitis were remained. Conclusion: It could be concluded that in patients less than 4 years of age with recurrent infection, analysis of serum gamma globulin levels and Btk gene are recommended for the early diagnosis of XLA and for appropriate prevention of recurrent infection.