Conceptually, thyroid disorders can be classified into four groups, namely: 1. disorders of thyroid morphology, 2. disorders of thyroid function, 3. presence of thyroid autoimmunity, and 4. diagnosis and follow-up of thyroid carcinoma. Of course, these groups are non-exclusive, and often there is overlap between the groups. Ultrasound exam is a standard for the diagnosis of the disorders of thyroid morphology. To diagnose disorders of thyroid function TSH and thyroid hormones should be measured. Presence of thyroid autoimmunity is confirmed by measuring antibodies against thyroid-specific antigens. Thyroid peroxidase (TPO), thyroglobulin (Tg) and TSH receptors antibodies are used in the diagnosis, follow-up and prognosis of autoimmune thyroid disorders. The measurement of serum thyroglobulin has no role in the diagnosis of thyroid cancer, but it is used in the follow-up of patients treated for differentiated thyroid carcinoma of the follicular epithelium. Medullary thyroid cancer (MTC) produces calcitonin and carcinoembryonic antigen (CEA), but calcitonin is specific for MTC. In subjects with MTC, genetic testing should be done, and in positive cases family screening is necessary.