OBJECTIVES: Since 2006, data on migration status is collected through representative survey in Chile (CASEN-survey). In this survey, around 1% reported being international immigrants in this survey; however, 0.67% preferred not to report their migrations status. This study aimed at exploring the living conditions and health status of migration status missing values (MS-MV) and compare them to self-reported immigrants in this survey. METHODS: Design: Cross-sectional analysis of population-based CASEN survey-2006 in Chile (268,873 participants). This analysis focuses on the 0.67% that did not respond the question on migration status (MS-MV) (n=1577) versus self-reported international immigrants (n=1877). Six health outcomes: any disability (dichotomous), any health problem/accident (AHPA), any hospitalization/surgery (AHS), any chronic condition/cancer (ACCC), and any medical and emergency attentions. Living conditions: Demographic factors (age, sex, marital status, urban/rural), socioeconomic status (household income per capita, employment status and educational level), and material standards (overcrowding, sanitation index, housing quality standards). Weighted crude and adjusted regression models were conducted in STATA 10.0. RESULTS: The MS-MV has a higher rate of children, especially with an ethnic background, and people living in rural settings than immigrants. They show a lower SES (income, education and type of occupation) and poorer material living conditions than immigrants. The MS-MV show a higher rate of emergency attentions received in the past month, disability, and AHS than immigrants. Other health events were not different between these two population groups. CONCLUSIONS: The MS-MV represents a complex group, affected by socioeconomic deprivation. Some of them may be undocumented immigrants, but there is little direct evidence to support this. Regardless of their migration status, this is a vulnerable group that needs special consideration in Chile. Equity-centred policy interventions in Chile should focus on improving the living standards and protecting the health of those were categorised into this group, particularly the children.