- Background A recent mumps outbreak in Israel despite an ongoing national program of a 2-dose universal childhood vaccination policy since 1988, raised questions regarding population immunity among young adults. Objective To assess the seroprevalence of mumps antibodies among young Israeli adults born after 1987 in order to determine evidence based vaccination policy. Methods We conducted a seroprevalence study of mumps IgG antibodies among 441 Israeli adults born in 1988–9, based on a representative sample of sera collected upon recruitment to mandatory military service in 2007. Results The overall seroprevalence of IgG antibody to mumps virus among 1988–9 born was 83.7%, 82.1% among males and 85.7% among females. Seroprevalence among 2007 recruits was similar to 1999 recruits (83.3%, P = 0.89) and significantly lower than 1987 recruits (94.1%, P < 0.0001). The absolute decrease between 2007 and 1987 for males was 13.1% (P < 0.0001) and for females 7.0% (P = 0.02). Seroprevalence was not significantly higher among native Israelis (84.9%) than among young adults born in the Commonwealth of Independent States (81.1%, P = 0.46) and significantly higher compared to young adults born in Western Europe or North America (68.2%, P = 0.045). Conclusions Our findings indicate sub-optimal population seroprevalence despite a 2-dose universal childhood vaccination policy. This study allows better understanding of current mumps outbreaks in Israel and elsewhere following periods of low circulation of wild virus. These findings support mumps vaccination, even for populations and individuals that received two doses during childhood, as means for outbreak containment among young adults, especially in crowded settings, and serve as a reminder to the need for dynamic vaccination policy, supported by health promotion activities.