To evaluate whether the diagnosis of X-linked agammaglobulinemia (XLA) is being made in a timely fashion, the clinical findings leading to the diagnosis of XLA were determined in 82 patients with proven mutations in Bruton's tyrosine kinase (60 patients with sporadic disease and 22 patients with familial disease). Recurrent otitis was seen in almost all of the patients with sporadic XLA who were older than 12 months at the time of diagnosis. However, fewer than 10% of patients were evaluated for immunodeficiency before they were hospitalized for infection; 38% of patients were hospitalized more than once before diagnosis. We conclude that the majority of patients with XLA were recognized to have immunodeficiency during or shortly after their first hospitalization for infection. Most of the patients had a history of recurrent otitis at the time of diagnosis, which when combined with the physical finding of markedly decreased or absent tonsils and cervical lymph nodes, could have alerted physicians to the diagnosis of XLA.