Basics -- The Changing Epidemiology of Thyroid Cancer -- Histopathology, Immunohistochemistry, and Molecular Biology -- Familial Differentiated Carcinoma of the Thyroid -- The Diagnosis of Thyroid Cancer -- The Current Surgical Approach to Non-Medullary Thyroid Cancer -- Differentiated Thyroid Cancer -- Radioiodine Therapy for Thyroid Cancer -- 124I Positron Emission Tomographic Dosimetry and Positron Emission Tomography/Computed Tomography Imaging in Differentiated Thyroid Cancer -- External Beam Radiotherapy -- Thyroid Cancer: Treatment with Thyroid Hormone -- Treatment with Cytotoxic Drugs -- Redifferentiation Therapy of Thyroid Carcinomas with Retinoic Acid -- Follow-up of Patients with Well-Differentiated Thyroid Cancer -- Thyroglobulin as Specific Tumor Marker in Differentiated Thyroid Cancer -- Functional Imaging of Differentiated Thyroid Cancer -- Magnetic Resonance Imaging -- Thyroid Cancer in Chernobyl Children -- Medullary Thyroid Cancer -- Diagnosis of Medullary Thyroid Cancer -- Imaging in Medullary Thyroid Cancer -- Therapy for Medullary Thyroid Cancer -- Follow-up of Medullary Thyroid Cancer.One of the main reasons for publishing this second edition of “T- roid Cancer” is the fact that the first edition has sold out. Furth- more, during the 4 years following the publication of the first edition in 2001, some progress, mainly in the basic sciences (molecular biology), has been made. The most prominent change in the clinical sciences has been the new classification of thyroid cancer, especially with relation to T1–T3 tumors. Now, tumors with a diameter of up to 2 cm are still classified T1. This new UICC classification (6th edition) follows the classification of the American Society of Pathology. These changes require a modification of the old guidelines. According to the Hedinger classification (1988) tumors with a diameter below 1 cm were classified as “papillary microcarcinoma of the thyroid”. Only in those tumors was total or nearly total thyroidectomy deemed unn- essary and I-131 therapy not a prerequisite for treatment. The majority of the chapters has been updated including references to many new publications. Two new chapters, on I-124 PET and - simetry, have been added. We strongly feel that this second edition of “Thyroid Cancer” is again a state-of-the-art overview of the diagnosis and treatment of thyroid cancer. Bonn, Frankfurt am Main H. -J. Biersack, F. Grünwald Preface to the First Edition Thyroid cancer was first described at the end of the eighteenth c- tury.