In 1989, in response to multiple outbreaks in the context of routine administration of a single dose of MMR during childhood, the ACIP recommended routine administration of 2 doses of MMR vaccine, with the first dose administered at ages 12 through 15 months and the second at ages 4 through 6 years. The administration of 2 doses led to a decrease in the number of measles cases as well as mumps nationwide. Due to increase in mumps in 2006, the ACIP recommended that adults with potential exposure to measles and mumps receive a second dose of MMR, including college students and health care personnel. In 2016, the number of mumps cases (6,369) was the highest in over a decade, with the vast majority occurring in the setting of outbreaks. 50% of outbreaks occurred in universities and 11% in other close-knit communities. Most were manifest by parotitis, but approximately 3% had other mumps complications including orchitis (75% of complications), aseptic meningitis, and rarely encephalitis. Given the increase and clustering of cases, the ACIP has recommended an approach driven by public health authorities, where the public health network will define target groups at increased risk for mumps during the outbreak, determine whether vaccination of at-risk persons is indicated, and provide recommendations for vaccination to health care providers. — Neil Skolnik, MD