Common variable immunodeficiency (CVID) is the commonest symptomatic primary antibody deficiency syndrome. The predominant manifestation is hypogammaglobulinemia. CVID is characterized by recurrent bacterial infections, especially of the upper and lower respiratory airways, and is also associated with an increased incidence of autoimmune and neoplastic disorders. Most patients are diagnosed as adults and delay in the recognition of the disease is common. Several T and B cell defects have been described, although the underlying cause is still unknown.