What episode number was Pokémon’s controversial Porygon episode?

Pokémon’s controversial Porygon episode was episode 38 of the first season.

Titled Dennō Senshi Porygon, or Computer Warrior Porygon, the episode was broadcast in Japan on December 16, 1997. Its story sends Ash and his friends into cyberspace to investigate a malfunction involving a Pokémon Center’s Poké Ball transmission system.

Flashing red and blue visual effects during the broadcast caused photosensitive seizures and other symptoms among viewers. More than 600 people were taken to hospitals, and the Pokémon anime then entered a lengthy hiatus in Japan.

The episode was never rebroadcast and was not included in the regular international television release. Although the incident is commonly called the “Porygon episode,” Pikachu’s Thunderbolt sequence produced the flashes; Porygon itself was not responsible for the visual effect.