The fundamental requirement for ultrasound in thyroid disease is to differentiate cystic masses from solid ones. But with the advance in scan equipment and technique the more detailed information about the lesion, echogenicity, internal echo pattern and surroundings casts but a faint light on the clues to give more specific categorical or histological diagnosis of the lesions. Authors reviewed 186 cases of ultrasonography of thyroid gland performed from March to September, 1979 at Seoul National University Hospital and concluded that ; 1. Differentiation of solid mass from cystic one is easily and readily made but a few of solid masses appear as cystic ones in ultrasonogram because of inappropriate scan technique. 2. Categorical or histological diagnosis is still beyond the scope of our knowledge but some clues suggest that only accumulation of data will solve the problem in the future.