Idiopathic CD4+ T-lymphocytopenia (ICL) is a new disease entity characterized by CD4+ T-lymphocyte depletion without evidence of HIV infection. We report a 27-year-old ICL patient with a long history of multiple immune abnormalities. His CD4+ T-lymphocyte count started to decrease after generalized lymphadenopathy of an unknown cause at age 3. He satisfied the criteria for ICL at age 9, and the decreased CD4+ T-lymphocyte count persisted for more than 18 years. This is probably the first childhood-onset ICL case in which the trigger event for the development was known together with the patient's autoimmune background.