To the Editor: Italian military recruits have received mandatory mumps vaccination by Urabe Am9 strain since 1998. A previous study1 found that, in 1999, 37 episodes of mumps-like disease were found in recipients of the vaccine, and that 35 of these occurred within 1 month of immunization. To assess whether these cases were due to some expected residual virulence of the live attenuated Urabe Am9 mumps strain, we analyzed saliva samples from recruits who developed mumps-like disease within 1 month of vaccination.