The United States has achieved a >99% reduction in mumps through a remarkably successful routine immunization program and has previously set a goal of elimination of endemic mumps by 2010. Most of the world, however, is endemic for mumps. Many countries have no vaccination program for mumps, and others only require 1 dose of a mumps-containing vaccine, so the United States is at risk for virus importation and mumps outbreaks. Following a large-scale outbreak of mumps in the United Kingdom, 2004-06, the U.S. experienced a multi-state mumps outbreak in 2006, primarily in Midwestern states, caused by the same G genotype of mumps virus responsible for the U.K. outbreak. Subsequently, the maritime provinces of Canada (Nova Scotia, New Brunswick) and other provinces have experienced a large G-genotype mumps outbreak during 2006-07, and Maine is currently experiencing a mumps outbreak that began in the fall, 2007. Presenters in this workshop will discuss the epidemiology of mumps in the U.S. and these recent outbreaks that illustrate 1) the challenges of clinical and laboratory diagnosis of mumps in vaccinated populations; 2) difficulties in implementing control and prevention measures – including isolation & vaccination – when disease is not readily recognized and populations resist efforts because of perceptions that disease is mild and inconsequential. The implications of these events for U.S. mumps surveillance, outbreak investigation and vaccination policy will be discussed.