Acquired immunodeficiency syndrome (AIDS) in infants has different clinical and immunological characteristics from adult AIDS because of immunological immaturity of the fetus and newborn when infection is produced. Differential diagnosis with primary immunodeficiency diseases, mainly with severe combined immunodeficiency and hypogammaglobulinemia is often difficult, but clinical, epidemiological and immunological data aid in establishing diagnosis. Repeated bacterial infections and abnormal antibody production are common in such children and gammaglobulin therapy is indicated to prevent them and avoid continuous immunological stimulation that viral replication and disease progression.