The cytogenetic analysis of a patient with selective deficit of IgA and decrease in IgM, IgE, and IgG is presented. Using trypsin-Giemsa banding the karyotype showed monosomy 22 (45,XX,-22). The interest of this case lies in the rarity of the illness and in the association of monosomy 22 with hypogammaglobulinaemia and selective deficit of IgA, particularly as this chromosome is known to contain genes coding for immunoglobulin chains.