On what date did the Pokémon anime episode “Dennō Senshi Porygon” air in Japan?

The Pokémon anime episode “Dennō Senshi Porygon” aired in Japan on December 16, 1997.

The episode follows Ash and his friends inside a computer system while they investigate problems involving the Pokémon transfer system. A rapidly flashing sequence near the end used alternating red and blue light effects during an explosion.

After the broadcast, viewers reported symptoms including headaches, dizziness and seizures. Hundreds of people were taken to hospitals, and the incident led to the temporary suspension of the Pokémon anime and a review of television production practices in Japan.

The episode was never rebroadcast in its original form and was not included in the regular international releases. The incident is often called the “Pokémon shock.” Although Porygon appears in the episode, the flashing sequence involved Pikachu's attack, so blaming Porygon alone is an oversimplification.