Onychogryphosis (sometimes called "claw nail") is a disorder of the nail that is usually acquired but may be inherited. It most commonly affects the toenails, particularly the hallux. The nail plate presents as unevenly thickened, opaque, elongated, increased in curvature, often yellow-brown in color, and can show superficial transverse striations. The thickened nail can also be severely distorted and laterally displaced, giving it a shape like a ram's horn, causing pain and interfering with footwear and ambulation.

In the elderly population, the nail dystrophy is usually caused by microtrauma from poor-fitting footwear but is also seen with impairment of the peripheral vascularization, stasis dermatitis, onychomycosis, self-neglect, and orthopedic deformities such as hallux valgus and erectus.

Onychogryphosis may also be associated with injury to the matrix in patients with psoriasis or ichthyosis, diseases of the central nervous system, hyperuricemia, and impairment of the peripheral circulation.

Hereditary onychogryphosis has been rarely described. All the nails of both hands and feet may be involved. It is inherited as an autosomal dominant trait. Onychogryphosis has also been described as a feature of Haim-Munk syndrome, tuberous sclerosis, Papillon-Lefèvre syndrome, ichthyosis hystrix, and ectodermal dysplasia-syndactyly syndrome type 1.