Statement of the Problem: Early childhood caries is an important oral health issue. Finding its prevalence would predict the need for oral health promotion disciplines for specific age groups. Purpose: The aim of this study was to assess the caries experience of children living in Tehran, Iran. It also would evaluate the impact of gender, ethnicity, and socioeconomic status (SES) on this oral condition.Materials and Method: This epidemiological cross-sectional study was based upon stratified cluster random sampling. The samples consisted of 239 children (2- to 3- years old) registered in Tehran’s public healthcare centers for “Healthy Child Program”. Mothers of the recruited children were interviewed for the background data; then children were examined for the oral health status according to ICDAS-II (International Caries Detection and Assessment System) and WHO (World Health Organization) criteria. Statistical analyses were conducted using STATA.11 for SES classification considering six socioeconomic variables, and SPSS.21 for descriptive/analytical analyses.Results: Primary Component Analysis (PCA) demonstrated five classes of SES ranging from the lowest to the highest. The distribution of caries-free (CF) children was 10.87%, non-cavitated enamel caries (codes 01-02) were 28.03%, and about 61.1% had cavitated caries (codes 03-06). There was no significant difference in caries experience between the two genders. Cavitated lesions were more prevalent among Kurdish, who also had the least CF children. Caries prevalence, especially code 02, was more among children from 3rd class SES (moderate level). Gender, ethnicity, or SES had no impact on the CF status of the children; however, ethnicity showed significant impact on the prevalence of extensive caries (codes 05-06).Conclusion: The result of the present study is indicative of high caries prevalence among 2 to 3 years old children residing in Tehran. It highlights the need for comprehensive oral health promotion disciplines for this age group.