Objective To study the CT manifestations of thyroiditis. Methods CT findings on plain and contrast enhanced thin-slice CT scan of 36 cases with thyroiditis proved by surgery (34/36) or fine needle biopsy (2/36) were analyzed retrospectively.Results There were 28 cases of Hashimotos’ thyroiditis.The characteristic signs were seen in 68% cases (19/28).Plain CT scan showed diffuse and symmetrical enlargement of bilateral leaves and isthmus whith greately reduced density which was homgeneous or slightly heterogeneous,no calcification or lower density nodule was seen,conrast-enhanced CT scan demonstrated uniform enhancement which was more dense than adjacent muscles, the thyroid outline could be clearly defined and no lymphadenopathy was found. Symmetrical enlargement of bilateral leaves and isthmus with uneven density and multiple hyperdens nodules were presented in 1 case. 5 cases of Hashimotos’ thyroiditis associated with multinodular goiters revealed asymmetrical thyroid enlargement and uneven density on plain and conrast enhanced CT images. In 3 cases the thyroid gland was normal in size and shape,except for the reduced ,uneven density. Of these 3 cases,1 showed the enlargement of left lobe with a calcified nodule. There were 8 cases of subacute thyroiditis,the thyroids were asymmetrical enlargement ,strongly decreased in density with obscure margin and slight to intermediate enhancement.Conclusion CT is a very important modality for the diagnosis and differential diagnosis of various thyroidities.