X-linked agammaglobulinemia (XLA) is a rare genetic disease caused by a mutation in the Bruton tyrosine kinase (BTK) gene. It is characterized by a profound deficiency of B cells and a decrease in all classes of immunoglobulins (Ig). We report one case in a 3-year-old boy seen for recurrent acute otitis media, perineal abscess, oligoarthritis. The serum immunoglobulin (Ig) assay showed an IgG level of 0.6g/l. IgM and IgA are indosable. Marrow immunophenotyping showed an absence of precursor B less than 1%. Molecular biology confirmed Burton's disease (stop mutation, C37C) in exon 2 of the BTK gene. Treatment with intravenous immunoglogulin was started.