The rational treatment of thyroid diseases requires an understanding of the thyroid function and an accurate evaluation of its functional (endocrine), as well as it morphological alteration. There are several different imaging techniques which are available and are in use in the evaluation of thyroid diseases. In this article we present a protocol for the use of diagnostic imaging to evaluate a focal thyroid mass, a diffusely enlarged gland, regional, and distant metastatic disease. The current diagnostic applications of radionuclide scanning, ultrasound, computed tomography, and magnetic resonance imaging (MRI) will be discussed.