Ultrasound has proven to be helpful in the assessment of the thyroid gland and in particular of solitary hypofunctioning thyroid nodules. In 94% of cases differentiation can be made between solid and cystic lesions. This information is of importance to the clinician in deciding on the course of therapy. The ability to accurately measure thyroid gland size, the size of individual nodules, and to follow these with serial measurements during therapy, is also useful. Gray scale ultrasound may provide the additional benefit of differentiating between benign and malignant thyroid tumore. More study of this new technique is necessary before any final conclusions can be drawn as to its accuracy in the diagnosis of thyroid carcinoma.