Polydactylism is a common birth defect characterized by extra fingers or toes. Typically, the fingers and toes are just small bits of extra skin, but in some cases bone structure is intact and the extra digits are fully functional.

The condition is not life threatening and many parents choose to have the extra digit removed during infancy. Within the medical condition Polydactylism, there are several sub-categories. Preaxial polydactyly involves a second thumb. The thumb may be flush with the first or perpendicular to the hand. Postaxial polydactyly is an extra pinky finger.

Polydactyly is a symptom of several other disorders including Rubenstein-Taybi Syndrome, Pallister-Hall Syndrome, Mohr Syndrome, Meckel Gruber Syndrome, Ellis van Crevald Syndrome and Biemond Syndrome. Some animals are also born with polydactyly including cats, dogs, chickens and mice.

Famous people suffering from Polydactylism include Hound Dog Taylor (blues guitarist), Jimmy Cliff (reggae musician) and Hampton Hawes (jazz musician). In Hollywood fiction, Hannibal Lecter suffered from polydactylism. His condition was characterized as mid ray duplication polydactyly or two middle fingers.