Hand, foot, and mouth disease (HFMD) is a common viral illness caused by enteroviruses that predominantly affects children aged <5 years. In the United States, outbreaks of HFMD typically occur during summer and autumn months. The most common cause of HFMD in the United States has been enterovirus serotype coxsackievirus A16. Most infections are asymptomatic; persons with signs and symptoms typically have a mild febrile illness with rash on the palms of the hands and soles of the feet, and sores in the mouth. HFMD also has been associated, often weeks after initial symptom onset, with nail dystrophies (e.g., Beau's lines or nail shedding).