Introduction: Two folds increase in differentiated thyroid cancer (DTC) have been noticed in the past few decades. This might be linked to either increase in the exposure of individuals to environmental risk factors or improved diagnostic techniques or both of them. We aimed at studying risk factors of thyroid cancer in Sohag, Egypt. Methodology: retrospective case control study that was conducted in Oncology & Nuclear department of Sohag University Hospital in four months duration from July 2016 to October 2016.105 DTC cases were compared to 150 controls for presence of these risk factors (radiation, radioactive iodine, obesity, family history of thyroid cancer, previous thyroid nodule and smoking). Results: out of 105 DTC cases, 94.1% were females, 60.2% had papillary carcinoma. Compared to controls, obesity and positive history of thyroid nodule were found to be very high significant risk factors (P value <0.001), residence also showed significant difference between cases and control (P value <0.05). While no significant difference was found as regard smoking and positive family history of thyroid cancer. Conclusion: Ultra sonographic finding should be the corner stone in management of thyroid nodule in any patient whatever the age and increase awareness about hazards of obesity are needed especially among uneducated rural females.