Mumps is primarily a childhood illness that is caused by a virus .
The chief sign of mumps is swollen, painful salivary glands, especially directly behind and below the ears. Symptoms usually start out remembling the flu with a fever, headache and muscle aches. Then within a couple of days the swelling typically appears. It often begins on one side, but can spread to the other side or to other salivary glands. It takes a week or 10 days for the swelling to recede.