Three hundred and ten patients with solitary thyroid nodule were examined with ultrasonography. Then the findings were compared with pathological diagnosis. The shape and the size of nodules, the nature of the margin and the internal echo, and calcification were evaluated with interest. Comparing these ultrasonographic findings with pathological diagnosis, following conclusions were drawn; 1. The irregularly shaped, ill demarcated nodules and/or those with internal heterogeneous echo and/or calcification generally indicated papillary carcinomas. 2. Most part of papillary carcinomas can be differentiated from benign nodules ultrasonographically. 3. Follicular carcinomas are difficult to differentiate from benign nodules based on ultrasonographic findings.