Young adults are a high‐risk group for experiencing loneliness. We examine (1) the prevalence of loneliness among young adults in three ethnocultural groups in Israel: native Jews, former Soviet Union immigrants and Arabs; (2) the associations between loneliness and ethnicity, perceived poverty, physical and mental health, perceived discrimination, social capital and online social capital; (3) the distinct sensitivity of the three ethnocultural groups to the determinants of loneliness. Cross‐sectional representative data for individuals aged 20–34 were taken from the 2016 to 2017 Israeli Social Surveys (N = 4253). Hierarchical logistic models were estimated to predict loneliness. Differences in the prevalence of loneliness were observed among the groups, with immigrants at higher risk. We found both common and distinct risk factors among the groups and only little evidence for moderation. Ethnic differences in loneliness between the native Jews and the Arabs can be ascribed to differences in their demographic characteristics and the prevalence of other risk factors. The risk for loneliness remained higher for immigrants after controlling for the entire set of risk factors. Eliminating the possibility that immigrants are more sensitive to any risk factor considered suggests the effect of ethnicity per se or rather that other factors affect loneliness in young immigrant adults.