Aim: To estimate the prevalence of severe early childhood caries (s-ECC) in the primary dentition of young children in Ajman, UAE, and investigate its association with child and family characteristics, dietary habits, oral hygiene practices and dental services utilisation. Methods: A one-stage cluster sample was used to randomly select children aged five or six years old who were enrolled in public or private schools in Ajman, UAE. Clinical examinations for caries were conducted by a single examiner using WHO criteria. Parents completed questionnaires seeking information on child and family characteristics, dietary habits, oral hygiene, and dental service utilisation. Bivariate and multivariate analyses were used to identify risk markers and risk indicators for s-ECC experience. Results: The total number of children sampled was 1297. Dental examination and questionnaire data were obtained for 1036 (79.9%), of whom 50.0% were female. The overall prevalence of s-ECC was 31.1% (95% CI, 23.6, 38.9). The prevalence of s-ECC was higher among children of low-income families, those who had a high snack consumption level, and those who utilised dental services only when they had a problem. Conclusions: The prevalence of s-ECC in young children in Ajman is high, and socio-economic characteristics, dietary habits, and dental utilisation are important determinants of their dental caries experience. There is an urgent need for oral health programs targeted at the treatment and underlying causes of dental caries in these children.