The number of notified cases began increasing in 2003 and continued to increase during 2004-2005, accompanied by further increases in the proportion of confirmed cases. During 2004, a total of 16,367 cases were notified; 10,641 (65.0%) of these were tested for oral fluid IgM, and 6,047 of those cases (56.8%) were determined to be IgM positive. When combined with those cases confirmed by serum IgM testing, a total of 8,128 (49.7%) cases were laboratory confirmed during 2004, compared with 3,907 (29.9%) of 13,087 notified cases during 1999-2003. In February 2005, because of high rates of laboratory confirmation of cases among persons born during 1981-1986, the UK Health Protection Agency recommended a temporary halt to testing persons with notified cases of mumps born during those years,2 although persons in other age groups with lower rates of confirmation continued to be tested. Testing for all age groups resumed in January 2006 after a sustained decline in the number of notified cases in the last quarter of 2005.