Follicular thyroid carcinoma is the second most common endocrine malignant tumour. It occurs 3- 4 times more frequently in females than in males and usually presents in the 50–60 year age group as an asymptomatic thyroid nodule. Although it often invades vascular structures and causes hematogenic metastasis, the prognosis is good in the low stage. In most cases follicular thyroid carcinoma is a minimally invasive follicular thyroid cancer and almost 90% of the patients can be cured. For a more specific prognosis in individual cases there are several prognostic factors: age, gender, tumour size, local recurrences, vascular invasion and distant metastasis. Different combinations of these prognostic factors are used in several scoring systems which determine tumour stage and predict the clinical outcome. Tumour size is used in all of these scoring systems. It is considered to be a significant prognostic factor, since in tumours measuring 2 cm or more microscopic lymph node metastasis can be expected, and in those larger than 4 cm extrathyroid invasion and distant metastasis are more commonly present. Larger tumours have a worse prognosis, as they are associated with wider spread of the disease, lower disease-free survival, and higher mortality.