We studied a reported illness outbreak occurring on December 16, 1997, invo
lving more than 12,000 Japanese children who had various signs and symptoms
of illness after watching an episode of a popular animated cartoon, Pokemo
n. While photosensitive epilepsy was diagnosed in a minuscule fraction of t
hose affected, this explanation cannot account for the breadth and pattern
of the events. The characteristic features of the episode are consistent wi
th the diagnosis of epidemic hysteria, triggered by sudden anxiety after dr
amatic mass media reports describing a relatively small number of genuine p
hotosensitive-epilepsy seizures. The importance of the mass media in precip
itating outbreaks of mass psychogenic illness is discussed.