The seventh son of a seventh son is gifted as a healer. There are several alleged cases of an Irish healer in Scranton, Pennsylvania. Paul Joseph Cawley was a seventh son of a seventh son and was known in this coal mining town for allegedly healing many skin diseases. The seventh son of a seventh son is part of a more general phenomenon known as the "cure" (sometimes also called the "charm")
It is believed that the seventh son of a seventh will be born a werewolf or with magic powers.
According to Kendall'sTravels through the Northern Parts of the United States, in the year 1807-1808 while visiting the Newgate copper mine (and prison) the author met an innkeep who told him that "there was to be found in the surrounding hills, a black stone, of a certain species, through which a seventh son of a seventh son, born in the month of February, with a caul on his head, can discern everything that lies in the depths and interior of the globe." The author speculates that the importance of mining to the community gave rise to this localized belief 
Paraguay, Uruguay, and Spanish America
It is commonly believed that he will be a werewolf, "hombre lobo" or "lobizón". However this only applies to a seventh son, so a seventh son of a seventh son would result in a werewolf son of a werewolf.
In the NBC soap opera Days of Our Lives, the somewhat gothic and mystical international crime boss Stefano DiMera, who called himself "the Phoenix" and has "come back from the dead" (or rather, faked his death) countless times, has claimed to be the seventh son of a seventh son.
In the television series The Storyteller episode "The Luck Child" an evil king sets out to kill the seventh son of a seventh son who is prophesied to become king.
In the movie The Seeker, a boy, who is the seventh son of a seventh son, is charged with the duty of saving the world from being overtaken by darkness.
In the Discworld series by Terry Pratchett, magical properties are attributed to the number eight rather than seven. Traditionally on the Discworld, an eighth son of an eighth son becomes a wizard. A wizard's eighth son—the eighth son of an eighth son of an eighth son (an unlikely and deliberately discouraged event)—is a Sourcerer, a dangerously powerful wizard. In the novel Equal Rites, instead of an eighth son of an eighth son a daughter is born. The daughter inherits a wizard's staff and then receives the wizarding powers normally given to the eighth son. This causes problems as females are supposed to be witches, and males wizards. The powers associated with each title are not interchangeable. The novel Sourcery centers on the unlikely story of a wizard's eighth son – the Sourcerer.
Orson Scott Card's novel Seventh Son begins the series The Tales of Alvin Maker (Alvin is the seventh son of a seventh son; however, his siblings also include sisters that were born in the time between the birth of his eldest brother and himself. On the other hand, he is "born with the caul.")
Invisible Man by Ralph Ellison has a character named Wheatstraw who is the seventh son of a seventh son.
In the Septimus Heap series by Angie Sage, Septimus Heap is the seventh son of a seventh son, and as such is an extremely gifted wizard.
Comic booksuperheroJohnny Thunder obtained his magical birthright by virtue of being the seventh son of a seventh son. He was also born at 7 am on July 7 (the seventh day of the seventh month), 1917.
In The Wardstone Chronicles series by Joseph Delaney, only a seventh son of a seventh son can become a Spook, the man who's in charge of ridding the countryside of witches, boggarts and other things that go bump in the night. Twelve-year-old Tom, the last apprentice, triumphs over various scary circumstances and hardships on his way to fulfilling his destiny as a Spook.
In The Red Scarf, a novel by Kate Furnivall there are three sevenths of sevenths (an old gypsy man, a young woman who is the seventh daughter of the seventh daughter, and also a young boy). In this novel, the seventh-of-sevenths have powers of hypnotic type mind-control.
In the Frontier Magic trilogy by Patricia Wrede, the character Lan is the seventh son of a seventh son, and as a result has very strong magical abilities.
In Gloria Naylor's Mama Day the titular character is the daughter of a seventh son of a seventh son.
In John Morressy's Young Kedrigern and Search for the Past, the sevenths are pushed to the third generation; Kedrigern is the grandson of the White Wizard, whose mother of was the seventh daughter of a seventh daughter of a seventh daughter and the father was the seventh son of a seventh son of a seventh son; the pair had a septuplet, four boys and three girls, who all became sorcerers and sorceresses. The youngest child, the White Wizard, is in fact the seventh son of a seventh son of a seventh son of a seventh son, because before the septuplet the pair had other three boys.
Seventh Son Virus – a computer virus affecting COM files, the words "seventh son of a seventh son" appear in infected files.
The GIJoe character Crystal Ball is the seventh son of a seventh son, and has limited mind-reading abilities.