At the end of December 1990, a vaccination campaign with attenuated measles virus strain Edmoston Zagreb was started at USL 23, Arezzo. Subjects to be vaccinated as identified by assessment of individual susceptibility represented 45% of 9609 children aged between 13 month and 10 years. At the end of January 1991, with the vaccination campaign in full swing, two cases of measles were reported. Subsequently, the number of cases reported grew steadily with differences in number of cases and age of sick children between the various districts of USL 23. Variability of susceptibility to measles had in fact been observed between these districts associated with the different degree of compliance with the vaccination campaign. Therefore, by active motivation of the population, the vaccination campaign was stepped up, and after June 1991 no further cases of measles were recorded.