Health bosses in Cornwall have started a mumps awareness campaign with GPs, schools and colleges after a sharp rise in cases.
The Health Protection Agency and NHS Cornwall said cases so far this year were close to usual annual levels.
The number of cases in the first 18 weeks of 2010 reached 134. There were 153 cases in all of 2009.
The campaign has urged people in the area to check their immunisation history to ensure they are protected.
Health bosses said the number of cases of the virus had raised concerns that people were missing out on the MMR (measles, mumps, rubella) vaccine.
Lee Evans, from the Health Protection Agency in Cornwall, said: "We have seen a sharp rise in the figures this year, and there is evidence that the disease is hitting two age groups the hardest: primary and junior school children, and 16 to 25-year-olds.
"The situation is widespread throughout the county with hot spots in the large towns, Penzance, Truro and the St Austell/Bodmin areas.
"That is why we are working closely with the schools and colleges to inform students about mumps and to explain why vaccination is important."
He added: "It's not just students who are at risk and we would urge everyone up to the age of 25 to consult their family doctors about having two doses of MMR vaccine if they are currently unprotected."
Mumps is spread by coughs and sneezes and directly through close personal contact.
Symptoms include swelling on the angle of the jaw on one or both sides of the face.
Often there are several earlier days of symptoms, which could include fever, headache, tiredness, muscle aches and loss of appetite.