Abstract: Objective To investigate the risk factors of thyroid cancer and to provide scientific basis for prevention of thyroid cancer.Methods A 1:1 matched case-control study was conducted.Two hundreds cases were chosen from inpatients with thyroid cancer diagnosed in Dalian city from 2008-2009 and the controls were chosen from inpatients without cancer and endocrine systemic diseases and hospitalized in the same hospital and the same period as the cases.A face-to-face survey was conducted with a self-desinged questionnaire.Results Univariate conditional analyses showed that liking salty food ten years ago,more consumption of seafood,seaweed,and pickled foods,with stress frequently,with pessimistic attitude,without harmonious marriage,and without good relationship with others were risk factors for thyroid cancer.The results of multivariate condition logistic regression analyses showed that eating too much seafood(odds ratioOR=9.484,95% confidence interval95%CI=3.868-23.256)and kelp ten years ago(OR=1.933,95%CI=1.209-3.092),being sulking easily(OR=3.804,95%CI=1.482-9.765),without good relationship with others(OR=2.460,95%CI=1.149-5.266)were the risk factors of the thyroid cancer.Conclusion Thyroid cancer incidence has close relationship with iodine intake and social psychological factors.