Full Text Article. Also available at: https://bmcnutr.biomedcentral.com/articles/10.1186/s40795-017-0163-1Background: Iodine deficiency is a widespread global health problem that affects about 2 billion people each year. Pregnant women are particularly vulnerable to iodine deficiency due to increased iodine requirement leading to death, miscarriage, and stillbirth. Iodine deficiency also has significant negative effects on newborns including impaired cognitive development, impaired learning capabilities, and stunting. This study looks at the association between subclinical iodine deficiency and demographic factors including age, wealth index, education, family size, geographical zone, number of children, fish consumption, pregnancy trimester and household salt in pregnant women aged 15–49 years in Tanzania. Methods: The 2010 Tanzania Demographic and Health Survey (TDHS) data was re analyzed. Subclinical iodine deficiency is classified as a urinary iodine concentration (UIC) of <150 μg/L. Results: Results showed that the prevalence of iodine deficiency (54%) was unacceptably high among pregnant women. The results of multiple logistic regression model found that number of children, wealth index, household salt, and geographical zone were significantly associated with iodine deficiency in these women. Conclusion: These results indicate a need to implement interventions to increase iodine intake that targets pregnant women with the specific demographic characteristics.