The Forgotten Frontier is a 1931 American documentary film about the Frontier Nursing Service, nurses on horseback, who traveled the back roads of the Appalachian Mountains of eastern Kentucky. It was directed by Mary Marvin Breckinridge, and featured her cousin, Mary Breckinridge, who was a nurse-midwife and founded the Frontier Nursing Service. Also featured are the people of Leslie County, Kentucky, many of whom reenacted their stories. The film was shot with a hand-cranked camera, often in extreme climate. Stills created during the film's production are available at the Library of Congress. A soundtrack was added in the 1990s by the Library of Congress. In 1996, this film has been selected for preservation in the United States National Film Registry as being deemed "culturally, historically, or aesthetically significant films". Footage from the film was used in the 1984 documentary Frontier Nursing Service.