The immunodeficiency, centromeric instability, and facial anomalies (ICF) syndrome is characterized by hypogammaglobulinemia and recurrent bacterial infections. Here we report a novel case of ICF syndrome with hypogammaglobulinemia and an inverted CD4/CD8 ratio. Cytogenetically abnormal cells,that were identified in both CD4+ and CD4- peripheral blood lymphocytes, retained their ability to proliferate in vitro following polyclonal stimulation. A primitive defect of B-cell differentiation was detected.