A study of routine data on mumps in England and Wales suggests that its epidemiological features are changing from those of an epidemic disease in young adults and older children to a more endemic disease in younger children. Infection now occurs at an earlier age, at which complications are less frequent and symptomless infection may be more common. The incidence of clinical disease may be falling. The high proportion of registered deaths in the middle aged and elderly may be an artifact due to misclassification of causes of death and to misdiagnosis. These changes lessen the need for routine immunisation. Indeed with low acceptance rates of measles vaccination of 50% at age 15 months, mumps/measles routine vaccination at the same age is contraindicated because similarly low acceptance rates might lead to an increase in the number of cases of mumps in older children and young adults, at which ages complications are more frequent.