BackgroundJapan is famous for its fabulous creatures (yōkai) characterized by their deformities.MethodologyWe wanted to know if local factors were involved in the high frequency of these legendary malformations, and sought to identify local teratogenic elements.Results/discussionMany potential teratogenic elements have been identified, which can be linked to specific malformations (cyclopia, for example).Conclusion/perspectivesWe therefore confirm that local factors would indeed promote the development of cyclops in Japan. This might explain the great frequency of supernatural creatures exhibiting this physical characteristic within Japanese folklore, and who would transmit this empirical knowledge through the generations.