Ultrasonography is a useful tool for diagnosis diseases of the thyroid gland. The method is reliable, inexpensive and of high diagnostic efficiency. The structural information provided by the ultrasound technique complements the results of laboratory tests and other in-vivo techniques. The article reviews the indications, the accuracy and the usefulness of conventional and Doppler ultrasonography in the diagnosis of thyroid diseases. In our opinion ultrasound examinations should immediately follow the patient's history and physical examination. Additional in vivo methods should be performed according to the specified problems.