Forty-one adults (mean age 33) with a definitive diagnosis of X-linked agammaglobulinemia (XLA) completed a questionnaire concerning current and past medical problems and quality of life. Thirty-six of the 41 were working full time or were full time students; 18 had not missed any work or school due to infection in the previous year. Their quality of life was equivalent to that of the general US male population. Thirteen of the 41 reported that they had chronic lung disease, and 33 indicated that they had one or more episodes of sinusitis in the preceding year. Arthritis, diarrhea and skin infections were common but not debilitating. The 41 study subjects were more likely to have a prior family history of XLA, and they were more likely to have milder mutations in Btk, the gene responsible for XLA. These results indicate that most adults with XLA are moderately healthy and lead productive lives.