The indolent course of most thyroid papillary carcinomas, even the presence of regional lymph node metastasis, make them unique among human malignant head and neck cancers. Age, sex, extracapsular invasion and anaplastic change are known to be correlated with prognosis. The purpose of this study is to clarify the significance of DNA content analysis as a prognostic factor. Twenty five thyroid papillary carcinomas were possible to be examined by flow cytometric analysis using fresh surgical specimens and three nodular hyperplasias and seven follicular adenomas were included as control group. The results were as follows: l) All of twenty five thyroid papillary carcinomas showed diploidy. 2) S-phase fraction was $1.94{pm}2.77%$ in normal control group and $2.60{pm}2.66%$ in papillary carcinoma group. The proliferation index was $8.44{pm}3.89%$ in normal control and $7.70{pm}3.63%$ in papillary carcinoma group with even low value. 3) Age, sex, extracapsular spread and lymph node metastasis showed no significant difference. In conclusion, low proliferative activity of thyroid papillary carcinomas are thought to be related with good prognosis.