- Background The risk factors of underutilization of childhood vaccines in populations with high access to health services are not fully understood. Objectives To determine vaccination coverage and factors associated with underutilization of childhood vaccines in a population with sub-optimal vaccination compliance, despite a high health care access. Methods The study was conducted among 430 children from ultraorthodox Jewish communities in the Bnei Brak city and Jerusalem district. Data on immunization status, socio-demographic factors and on parents’ attitudes regarding vaccines were obtained from medical records and through parents’ interviews. Results The proportion of fully vaccinated children was 65% in 2- to 5-year-old ultraorthodox children from Jerusalem district, and 86% in 2.5-year-old children from Bnei Brak city. The factors that were significantly associated with vaccines underutilization in Bnei Brak were having >6 siblings, maternal academic education, parental religious beliefs against vaccination, perceived risk of vaccine preventable diseases as low, and mistrust in the Ministry of Health (MOH). Similarly, in Jerusalem, religious beliefs against vaccination, and the perceived low risk of vaccine preventable diseases significantly increased the likelihood of under-immunization, while having a complementary health insurance was inversely related with vaccines underutilization. Conclusions The risk factors of under-immunization are in part modifiable, by means of health education on the risks of vaccine preventable diseases and by improving the trust in the MOH. The leaders of the ultraorthodox communities could play an important role in such interventions.