The number of teenagers and young adults getting mumps has been increasing in Greater Manchester, health chiefs said.
The Health Protection Agency (HPA) North West recorded 27 cases in the past week, compared to the usual weekly average of 10-15 cases.
It advised unprotected teenagers and young adults under 25 to ask for vaccination with the MMR vaccine.
The increase has been put down to young people not having the MMR jab.
Doctor Rosemary McCann, consultant with the HPA's Greater Manchester Health Protection Unit, said: "Mumps appears to be increasing and teenagers and young adults aged 14-25 who have not previously had two doses of MMR vaccine are vulnerable. They should consult their GPs and arrange to be protected now. It isn't too late.
"Mumps is a serious disease that should not be taken lightly. It can be painful and it can lead to complications such as viral meningitis and inflammation of the testicles in men and the ovaries in women."
The symptoms of mumps are: painful inflammation and swelling of the salivary glands under one or both sides of the jaw, fever and headache.