The role and the different technical modes of ultrasound in thyroid autonomy are discussed. B-mode sonography is routinely employed to e.g. calculate thyroid and nodule volume, describe the echo pattern of both the thyroid gland and focal lesions and to visualize neighboring organs such as lymph nodes. Sonography thus possesses a complementary role to scintigraphy, since it may further aid in the localization of toxic adenomas, in particular when they are dorsally located or it may change the therapeutic decision. An example for the latter would be the preference of a surgical approach in case of cystic degeneration of an autonomously functioning nodule. Recently, color-coded doppler sonography using color flow mapping has been employed. With the advent of this technique it has become possible to describe the pattern of vascularization in thyroid focal lesions such as rim perfusion or internal hypervascularization. This technique harbors a high sensitivity for toxic adenoma exhibiting high internal blood flow, but does not appear to reliably discriminate between benign and malignant lesions. Nevertheless, further improvement of this technique may be promising in further characterizing the functional status of sonographically detected lesions and in the prognostic assessment of post-treatment outcome.