X-linked agammagobulinemia (XLA) is a primary immunodeficiency disorder caused by a mutation in the Bruton Tyrosine Kinase (BTK). Usually, patients present severe infections before the age of 2, and require immunoglobulin replacement therapy during all their life. We present the case of a 16-years-old male for whom the diagnosis was incidental. He did not present any infection since childhood. At the age of 4, immunoglobulin assay was performed because he had recurrent fever episodes. A panhypogammaglobulinemia was identified, but the boy became asymptomatic and explorations were stopped. At the age of 16, the patient’s parents suggested a control of the deficit which was confirmed. Genetic testing revealed a novel mutation on BTK, located in the pleckstrin homology domain [c.70A>C, p.(Asn24His)]. Initially, he received immunoglobulin substitution at the rate of one subcutaneous injection per week but stopped it after 2 years of treatment by immunoglobulin and continued to present no symptom. We thereafter report the case of an asymptomatic patient presenting a novel missense mutation of BTK. The patient doesn’t have circulant B cell. He doesn’t receive immunoglobulin substitution and doesn’t present infectious diseases.