1. acquire the environmental iodine status of Hangzhou
2. acquire the iodine status of population in Hangzhou
3. acquire the prevalence of thyroid diseases in Hangzhou
4. explore the association between iodized salt and thyroid disease

Inclusion Criteria:

1. age ≥ 6 years old;
2. living for above 5 years at present residence.

Exclusion Criteria:

1. resident with coronary angiography (CAG) or endoscopic retrograde cholangiopancreatography (ERCP) in 6 months;
2. resident taking amiodarone drug;
3. resident with abnormal kidney function or serious illness

This study was conducted in Hangzhou, Zhejiang Province, China, which locates at east of China. This city covers eight districts and five counties. There are 8.7 millions residents in Hangzhou city; 73.25% of them living in urban areas, 26.75% in rural areas. This study was designed to be representative of the civilian from Hangzhou and collected information on demographic characteristics, health status, iodine intake and thyroid disease.