X-linked agammaglobulinemia (XLA) is a humoral primary immunodeficiency. XLA patients typically present with very low numbers of peripheral B cells and a profound deficiency of all immunoglobulin isotypes. Most XLA patients carry mutations in Bruton tyrosine kinase (BTK) gene.The genetic background and clinical features of 174 Chinese patients with XLA were investigated. The relationship between specific BTK gene mutations and severity of clinical manifestations was also examined. Mutations were graded from mild to severe based on structural and functional prediction through bioinformatics analysis.One hundred twenty-seven mutations were identified in 142 patients from 124 families, including 45 novel mutations and 82 recurrent mutations that were distributed over the entire BTK gene sequence. Variation in phenotypes was observed, and there was a tendency of association between genotype and age of disease onset.This report constitutes the largest group of patients with BTK mutations in China. A genotype-phenotype correlation was observed in this study. Early diagnosis of congenital agammaglobulinemia should be based on clinical symptoms, family history, and molecular analysis of the BTK gene.