The aim of the present paper is to summarize the history of the Yusho incidence that occurred in the western part of Japan in 1968. A strange disease was reported in October 1968. This strange disease was characterized by acne-like eruptions, pigmentation of the skin, and eye discharge, and it was named Yusho (oil disease). Through systematic epidemiological studies based on observation of initial case series, and extensive efforts to clarify causal agents by the Study Group for Yusho, it was concluded that Yusho was caused by ingestion of rice oil contaminated with PCBs and PCDFs. As of now, more than 1,800 patients, have been registered as having Yusho and around 300 are deceased. Clinical observation showed that typical symptoms of Yusho have decreased, even general fatigue, headache and numbness of extremities have still been complained by patients. No effective treatment has been found so far. Careful and systematic observation for Yusho patients and medical care services should be continued for a further understanding of Yusho.