Objective: We aimed to assess the correlation of tumor size with other risk parameters in differentiated thyroid carcinomas. Material and Methods: Data of patients diagnosed with thyroid carcinoma, underwent bilateral total/near total thyroidectomy and treated with high doses of 1311 were examined retrospectively. In patients with tumor size <= 1 cm and >1 cm, the correlation between the tumor size and histopathologic classification, gender, age, multifocality and lymph-node was assessed. Results: The study included 285 patients; 237 (83.2%) were female, 48 (16.8%) were male. Two hundred and forty five patients (86%) had papillary carcinoma. The tumor was <= 1 cm in 6out of 23 male cases with a single focus (26.1%) and in 5 out of 14 male patients with multiple foic (35.7%). In those with tumor <= 1 cm multifocality rate was higher. In 32 out of 97 (33%) patients with tumor size <= 1 cm the tumor was multifocal, while in 46 out of 116 (39.7%) with tumor >1 cm there was uptake in many foci. For multifocality there was no significant difference for tumor size <= 1 cm and >1 cm (p=0.31). Of 65 patients aged >= 45 with a single focus, tumor size was <= 1 cm in 37 (56.9%), whereas in 21 out of 32 (65.6%) with multifocality, the tumor was <= 1 cm. In the patient group aged >= 45 the rate of multifocality was higher in those with tumor size <= 1 cm than those with tumors >1 cm. Conclusion: Although in patients with tumor size <= 1 cm and with no risk factor, lobectomy and isthmectomy is adequate and ablation therapy is not recommended, due to the high rate of multifocality, we suggest that total thyroidectomy and ablation therapy may be useful.