In a 30-year-old man, bilateral Kirner's deformity has been diagnosed. In the fully extended finger, the long axes of the middle and terminal phalanges formed an angle of 10 degrees in the volar and 5 degrees in the radial direction. Owing to the altered morphology of the distal phalanx, its palmar surface was at an angle of 25 degrees to the long axis of the middle phalanx. The deformity has existed since birth and has not changed except in size. His mother had the same bilateral deformity. Other closer relatives showed a unilateral appearance of Kirner's deformity: his maternal grandmother and an uncle had in their right little finger and an aunt had in her left little finger. Although some authors reported that Kirner's deformity was progressive, the description only referred to a change in the deformity. Kirner's deformity may be classified according to its period of onset, i.e., a more frequently occurring early type and a late type of onset (with lower incidence) exists. Moreover, it can be further classified by typical morphologic changes as well as the family history of the affected person.