Introduction. A study has been made of the behaviour of preventable infectious diseases by means of vaccination in the developmental age, reported between 1995 and 2003, in the area of Frosinone and Province, Italy. Results. Analysis of the distribution of the 185 cases of hepatitis B notified, demonstrates that the mean age has increased from 26.5 to 41.1 years. Notifications of invasive diseases due to hae- mophilus influenzae type b (Hib) refer exclusively to 13 cases of meningitis. As far as concerns pertussis, 119 cases have been reported (median age 4.0 years, mode 1.0). Overall 850 cases of measles were reported (median age 7.0 years, mode 5.0), the highest number being recorded in 1997 (349 cases: median age 7.0 years, mode 5.0) and 2002 (199 cases: median age 8.0 years, mode 8.0). Rubella occurred in 411 cases (median age 12.0 years, mode 11.0), with 53.3% involving females. As far as concerns mumps,the last peak of the epidemic occurred in 2001 (median age 7.0 years, mode 6.0) with 137 cases. Discussion and conclusion. Results emerging from the study dem- onstrate a reduction in time in the number of notifications for almost all the diseases under consideration. The distribution of the cases of rubella in fertile females, in 2002, stresses the need to promote campaigns in order to recuperate still-susceptible women of childbearing age. The cases of hepatitis B, pertussis and meningitis due to Hib confirm the high rate of protection resulting from vaccination. The incidence rates of measles, mumps, rubella and pertussis when compared with those of the paediatric sentinel surveillance system (SPES) clearly demonstrate not only that these are underestimated but also reveal controversial findings with respect to data provided by Infectious Diseases Italian Surveillance System (SIMI).