Aim: To study the ultrasonographic (US) differences between "mununified" thyroid nodules and malignant thyroid nodules in order to achieve a more accurate imaging-based diagnosis and to avoid unnecessary biopsy. Material and methods: We retrospectively reviewed the US features of mummified thyroid nodules, as confirmed by fine-needle aspiration cytology (FNAC), in 193 cases. The US features included content, echo, shape, margin, microcalcification, suspicious lymph nodes and some characteristic features, including the cystic wall shrinkage sign, the concentric configuration or finger sign, calcification and halo. All of these features were classified and compared with those of 109 malignant lesions. The changes of these mummified nodules during the follow-up period were also examined. Results: The cystic wall shrinkage sign and the concentric configuration or finger sip were highly specific indicators of mummified thyroid nodules and could be used to distinguish mummified nodules from thyroid cancer with a specificity of 91.7% and 99.9%, respectively. A continuous decrease in the cyst size was observed during follow-up. Conclusions: Mummified thyroid nodules are characterized by the cystic wall shrinkage sign and the concentric configuration or finger sign on US and a continuous decrease in size during follow-up. These features may be useful for the differential imaging-based diagnosis of mummified versus malignant thyroid nodules.