Yellow nail syndrome (YNS) is a rare disorder of unknown aetiology that is characterized by yellow nails associated with lymphoedema and chronic respiratory manifestations. There are no detailed immunological studies in YNS. In this study, we present first extensive immunological analysis of both adaptive and innate immunity in two patients with YNS. One patient has common variable immunodeficiency, whereas second patient has specific antibody deficiency syndrome. Severe lymphopaenia, a striking deficiency of naïve CD4+ and CD8+ T cells and total B cells, and increased transitional B cells were observed. T cell proliferative response to mitogens and antigens was significantly reduced in both patients. Both patients failed to make specific antibody response to pneumococci. Complement, natural killer cell activity and neutrophil oxidative burst were normal. Immunoglobulin administration resulted in decreased frequency and severity of infections, and an impressive effect was observed on lymphoedema and on the recurrence of pleural effusion. Our data show that YNS is associated with both T and B cell defects. Furthermore, Immunoglobulin may be beneficial in clinical manifestations of lymphoedema.