This is a case report and family study of a 65-year-old man with chronic prurigo lesions, in whom we demonstrated a selective deficiency of circulating T-helper/inducer lymphocytes (CD4+), in the absence of any apparent predisposing disease. He is seronegative for human immunodeficiency virus (HIV types 1 and 2) and human T-cell lymphotropic virus (HTLV-I and HTLV-II), and fulfils the criteria for the syndrome of idiopathic CD4+ T lymphocytopenia. He has an atopic diathesis, has had a severe adult chickenpox infection, chronic staphylococcal infections, tinea pedis and recalcitrant warts. He has also suffered from respiratory infections, for which no specific aetiological agent has been identified. His peripheral total lymphocyte count has been persistently abnormal since it was first measured in 1969. He has a marked CD4+ T-cell lymphocytopenia. His son, who does not have any skin disorder, has a low CD4+ T-cell count.