OBJECTIVE: To examine the relationship between acculturation and obesity among low socioeconomic status (LSES) children. DESIGN: Cross-sectional study. SETTING: Children from 12 preschools in LSES neighborhoods were recruited. PARTICIPANTS: Anthropometric measurements were obtained from 238 children (aged 4-7 years) and 224 mothers. Sociodemographic characteristics and perceptions of child's weight were collected from mothers. We compared native Israelis and immigrants for risk factors for obesity, using a 9-year cut-off to define new and acculturated immigrants. RESULTS: The combined prevalence of overweight and obesity (OWOB) among children was 29.8% (71/238) using the World Health Organization (WHO) growth standard. Mean age, sleeping hours, sex distribution and poverty level were similar between immigrants and natives. Prevalence of OWOB and current parental smoking were significantly lower among children of new immigrants (P = .02). More than 82% of mothers underestimated their child's weight status, 74.2% of OWOB children were perceived as normal-weight (NW) and 8% as thin. In a multivariable logistic-regression analysis comparing NW to OWOB children, maternal underestimation of the child's weight status (OR = 7.5; 95%CI: 3.4-16.5, P < .0001) and being born to acculturated immigrants (OR = 2.3 95% CI: 1.1-4.7, P = .03) were associated with OWOB. Ethiopian children were at lower risk for obesity. Paternal smoking increased the risk for obesity by 2-fold in non-Ethiopian, and 5-fold in Ethiopian children (OR = 2.0 and 5.0, respectively; P for interaction = .026). CONCLUSIONS: Acculturation, perception of child's weight status and parental smoking are associated with childhood OWOB. Immigration status should be considered when programs to prevent childhood obesity are implemented in mixed populations.