Subungual exostoses are a type of non-cancerous bone tumor of the chondrogenic type, and consists of bone and cartilage. It usually projects from the upper surface of the big toe underlying the nailbed, giving rise to a painful swelling that destroys the nail. Subsequent ulceration and infection may occur.

There is an association with trauma and infection. Diagnosis involves medical imaging to exclude other similar conditions, particularly osteochondroma. X-ray appearance may reveal a bony protuberance attached to the top or side surface of a toe bone.

Treatment is by surgical excision and is effective.

More than half are under the age of 18 years and males are affected equally to females. Combined with bizarre parosteal osteochondromatous proliferation, they comprise <5% of cartilage tumors.