"Dennō Senshi Porygon" (でんのうせんしポリゴン Dennō Senshi Porigon, translated as "Cyber Soldier Porygon", although more commonly "Electric Soldier Porygon") is the thirty-eighth episode of the Pokémon anime's first season. Its only broadcast was in Japan on December 16, 1997. In the episode, Ash and his friends find at the local Pokémon Center that there is something wrong with the Poké Ball transmitting device. To find out what is wrong, they must go inside the machine.
The episode is infamous for certain repetitive visual effects that induced photosensitive epileptic seizures in a substantial number of Japanese viewers, an incident referred to as the "Pokémon Shock" (ポケモンショック Pokémon Shokku) by the Japanese press. As a result of the seizures 685 viewers were taken to hospitals; 2 people remained hospitalized for more than two weeks. Due to this, the episode has not been rebroadcast worldwide. After the incident, the Pokémon anime went into a four-month hiatus, and it returned on TV Tokyo on April 16, 1998, thus making the episode perhaps the most controversial episode of the entire Pokémon series. Since then, the episode has been parodied and referenced in cultural media, including The Simpsons and South Park.