Diffuse thymic hyperplasia following chemotherapy for nodular sclerosing Hodgkin's disease is reported in an 18-year-old woman. The patient's course was complicated by drug-induced pulmonary fibrosis and disseminated herpes zoster. Subsequently she developed genuine diffuse thymic hyperplasia with disappearance of herpes zoster and apparently complete remission of Hodgkin's disease. We stress that restoration of the host immune system, particularly the cell-mediated immunity, is essential for successful control of Hodgkin's disease and the thymic hyperplasia is most likely a favorable sign for it, which should not be confused with recurrence of Hodgkin's disease.