Objective: To examine parent concerns about development, learning, and behavior for young children of Mexican origin, and to identify whether these reports differ by families' citizenship/documentation status. Methods: Data come from the 2005 California Health Interview Survey, a population-based random-digit dial telephone survey of California's noninstitutionalized population. California Health Inerview Survey (CHIS) investigators completed interviews of 43 020 households with a total of 5856 children under age 6 years, of whom 1786 were reported being of Mexican origin. Developmental risk was measured by parent concerns elicited by the Parents' Evaluation of Developmental Status. We used bivariate and multivariate analyses to examine associations between developmental risk and family citizenship/documentation status (parents are undocumented, at least one documented noncitizen parent, or both parents are US citizens) among children of Mexican origin and US-born non-Latino white children, after adjusting for age, income, parental education, and predominant household language. Results: In multivariate analyses, children of Mexican origin did not differ significantly from US-born white children in developmental risk (odds ratio 1.12, 95% confidence interval 0.88-1.42). In subgroup analyses, children of Mexican origin with undocumented parents had higher odds of developmental risk (odds ratio 1.53, 95% confidence interval 1.00-2.33) than non-Latino white children whose parents were citizens, after adjusting for confounders. Conclusions: Mexican children with undocumented parents have greater parent-reported developmental risk than Mexican and white children whose parents are US citizens or otherwise legally documented. More research is needed to understand the roles of immigration stress and home environments on the developmental risks of children in households with undocumented parents. © 2009 Academic Pediatric Association.