BACKGROUND Common variable immunodeficiency (CVID) is characterised by a late onset deficiency of immunoglobulins resulting in recurrent infectious and non-infectious ailments. Most cases are sporadic but occasional familial clustering has been described. We present an extensively affected family with CVID in three consecutive generations. METHODS We conducted a study in this family to establish clinical phenotype, to clarify the mode of inheritance and to attempt to characterise the immune disturbance by determining immunoglobulin concentrations and B- and T-cell analysis. RESULTS We describe six patients with CVID in three consecutive generations. In addition, we encountered 10 family members with dysimmunoglobulinemia. B-cell counts were normal, but T-cell analysis showed slightly abnormal results. CONCLUSIONS The six cases of overt late onset hypogammaglobulinemia are compatible with an autosomal dominant mode of inheritance. The family members with dysimmunoglobulinemia may be at risk to develop overt CVID in the future, in view of the gradual course of progression of the disease in the clinically affected family members. B- and T-cell analysis are inconclusive though may support a possible defect in T-cell function to be involved. To further study this remarkable family and attempt to clarify pathogenesis, we are planning DNA linkage analysis in the near future.