We experienced a case of pleural effusion while treating postherpetic neuralgia in a 70 year old male patient. The patient had scar and color change on the skin along the course of the right Th4-5 intercostal nerve, characteristics of healed herpes zoster. The patient also complained of severe pain along the lesion site which made sleeping difficult. He had been treated with; epidural blocks with or without catheterization; epidural or regional corticosteroids; multiple intraspinal and intercostal blocks with local anesthetic; or neurolytic, alcohol, transcutaneous electrical nerve stimulation, etc., for about six months by the time of pleural effusion development. We came to the conclusion that the effusion was due to pleural irritation by multiple intercostal nerve blocks, because it was bloody and developed on the affected right side, although the patient had a history of a certain hepatic pathology and pulmonary tuberculosis which may be a predisposing factor to the effusion.