We experienced two cases of malignancy diagnosed during the treatment of postherpetic neuralgia. One case was a lung cancer and the other case was a pancreatic cancer. Generally, herpes zoster frequently occurred in the patients who have immunosupressive disease, diabetes mellitus, malignancy and tuberculosis, etc. It is necessary to rule out malignancy in the patients who have herpes zoster, especially those patients whth severe eruptive cluster, persisting to the therapy or multifocal pain. So, we must carefully observe and follow up the patients to find out malignancy as well as to diminish the pain.