The circus sideshow was a smorgasbord of human performers, shrewdly designed to entertain the middle-class public and exploit the attitudes of the time. Under the vernacular of "pinheads," people with microcephaly and mental retardation were displayed as "freaks." This article presents original materials from the Ringling Brothers Circus Museum Archives and Harvard Theater Collection, including sideshow banners, circus programs, song lyrics, and performance photographs, in addition to contemporary newspaper articles, major medical journal publications, and other secondary sources regarding microcephaly in the 19th and early 20th century circuses. More than 20 performers were exhibited as "pinheads," popularly portrayed as "missing links" or children from lost civilizations. People with neurologic disorders were displayed as wild and juvenile and thus, joined a series of hoaxes of the American sideshow. Although incomplete data exist on their true lives, the exhibition of people with microcephaly eventually declined due to protective laws passed in part due to the American circus "freak shows."