The most common diseases of the toenails are caused by trauma, especially from chronic friction of the digits against each other or against the shoe. They are typically seen in adults with anatomical foot abnormalities. Onychomycosis of the toenails is also frequently seen in adults or elderly. Nail psoriasis may rarely localize exclusively to the toes, where it is rarely recognized, as it should be differentiated from onychomycosis. When one sole toenail is visibly altered in shape and size, the most likely diagnosis is onychogryphosis, but nail tumors should also be considered. The most typical nail tumor of the toenails is exostosis, a subungual bone tumor that affects almost exclusively the toe of adolescents and young adults.