Four hundred fifty cases of thyroid enlargement were studied by B-mode ultrasonography. Specific ultrasonographic patterns could be established for cyst, solid tumors, multinodular goiter, cystadenoma, and thyroiditis. Benign and malignant tissue could not be differentiated. In 155 cases, tissue diagnosis was established usually by operation but also by aspiration cytology. One hundred forty-two were hypofunctioning solitary nodules. The reliability of ultrasonographic diagnosis was 94%. It permitted safe aspiration of cysts, early operation of solid lesions, and avoidance of radiation hazard in the management of pregnant and pediatric patients. Our operative series showed the following incidences: cancer 16%, cyst 20%, and neoplasm 62%.