The mumps virus, globally endemic, is a member of the Rubulavirus genus in the Paramyxoviridae family. The virus is spread via direct contact with respiratory secretions and saliva. It can be transmitted via fomites. The incubation period is typically 1-2 weeks. Approximately 35% of cases are subclinical. A nonspecific prodrome consisting of fever, headache, malaise, and myalgia (especially the neck) may be seen. The characteristic onset (within 24 hours) of mumps is parotitis, either unilateral or bilateral, with the glands reaching their maximum size within 48-72 hours. Swelling does not typically last longer than a week. The area is tender and painful; pain can be elicited by eating or drinking sour substances such as lemon.

Mumps significantly declined in the United States after 1967, when the mumps vaccine was introduced, and again in 1977, when the vaccine was recommended for routine use. The incidence of mumps continued to decline with implementation of a two-dose MMR (measles, mumps, rubella) vaccine in 1989. The MMR vaccine prevents most, but not all, cases of mumps and complications caused by the disease. Two doses of the vaccine are 88% (range: 66%-95%) effective at protecting against mumps; one dose is 78% (range: 49%-92%) effective.

Mumps epidemics can still occur in communities of (even highly) vaccinated individuals in close contact, such as in dormitories and on sports teams, due to waning immunity after childhood vaccination allowing for breakthrough cases. Mumps outbreaks can occur any time of year. Mumps is rare in infants less than one year of age.

The prognosis is usually excellent, although, in rare situations, complications can occur including meningoencephalomyelitis, orchitis and epididymitis, oophoritis, pancreatitis, myocarditis, arthritis, thyroiditis, deafness, and dacryoadenitis and optic neuritis. The risk of spontaneous abortion is increased in women who contract mumps during the first trimester of pregnancy. Infection usually results in lifelong immunity.