Encephalitis lethargica first appeared during World War 1, but reported cases gradually faded over the 1920s, and in the years following, cases were only sporadically reported. The clinical presentation was heterogeneous and typically included both acute and chronic phases. The acute phase was characterized by excessive sleepiness, disorders of ocular motility, fever, and movement disorders. On the other hand, the chronic phase was characterized by Parkinsonism, oculomotor abnormalities, involuntary movements, speech and respiratory abnormalities, and psychiatric manifestations. In Peru, Espejo-Tamayo reported 47 cases of the disease between 1919 and 1924, with an average mortality of 13%. He described three waves of the epidemic in Peru: that of 1919, with a predominance of the lethargic-paralytic syndrome; that of 1920–1921, characterized by the algic-myoclonic syndrome; and the wave that began in 1922, when the disease acquired purely striatum syndromes, as well as those associated with the lethargic-paralytic and myoclonic syndromes and mental manifestations. We summarize six cases of encephalitis lethargica reported in Peru from 1920 through 1940.