Cyclin D1 protein was studied in 40 papillary thyroid cancer(PTC) patients including 24 cases of the conventional type, 12 cases ofits follicular variant and four cases of papillary microcarcinomaretrieved as routinely processed paraffin blocks taken from thedepartment of Pathology, Kasr El Ainy Hospital. For all specimens, someclinical data were available on the computer files including age and sex ofthe patients, tumor size, tumor focality, histopathological variant,presence of extrathyroidal extension and lymph node metastasis.Cell cycle progression is facilitated by Cyclin dependent kinases(CDKs) that are activated by cyclins, including Cyclin D1 and inhibitedby CDK inhibitors. Evidence of the involvement of Cyclin genealterations and overexpression of various cyclins in human cancer isgrowing. The role of Cyclin D1 in malignant progression of papillarycarcinomas of the thyroid has yet to be established.Using Immunohistochemistry, Cyclin D1 Expressors were consideredin cases exhibiting moderate or intense positive nuclear staining in ≥ 10of tumor cells. 20 patients (50 %) were considered Cyclin D1 Expressorsand 20 patients (50%) were considered Non-Expressors.A significant relation was detected between Cyclin D1 distributionand lymph node metastases. Also the relation between PTChistopathological variant and Cyclin D1 distribution was proved to besignificant (P value < 0.05).This does not rule out that the detected foci with positive nuclearCyclin D1 immunostaining are areas where a progressive transformationto a more malignant phenotype occurs which eventually leading to lymphnode and distant metastases.