Common variable immunodeficiency (CVI) is a heterogeneous syndrome characterized by defective antibody formation, resulting in abnormally low serum immunoglobulin levels. Clinical presentation usually includes recurrent infections of the respiratory tract, mostly induced by capsular bacteria. Patients are also highly prone to Giardia lamblia infections and related gastrointestinal disorders, as well as to a variety of autoimmune diseases which appear in approximately 20% of them. In addition, CVI can be frequently associated with a non-Hodgkin lymphoma or gastric carcinoma. In spite of its relatively frequent occurrence, the pathogenesis of CVI still remains poorly defined. In this review the authors describe clinical features, immunological abnormalities and replacement treatment with intravenous immunoglobulins of this antibody deficiency syndrome.