Boys affected with 49,XXXXY sex chromosomal variation have been described to have high incidence of recurrent otitis media and asthma, the cause of which is unknown. We hypothesized that primary immunodeficiency occurs in patients with XXXXY aneuploidy. To investigate this, 31 boys with known 49,XXXXY were evaluated through a multidisciplinary clinic. Screening history was performed using the “10 Warning Signs of primary immunodeficiency” (Jeffrey Modell Foundation), as well as by history of atopic and autoimmune conditions. Of the 31 boys, 20 had at least two warning signs of primary immunodeficiency, and five had four or more signs. Sixteen had history of recurrent pneumonia, and 15 carried the diagnosis of asthma. Of the 10 who underwent immunologic screening, eight showed some evidence of impaired antibody responses to polysaccharide antigens, and one was diagnosed with specific antibody deficiency. These preliminary results suggest a high incidence of both atopy and antibody deficiency in boys with 49,XXXXY. © 2013 Wiley Periodicals, Inc.