Flow cytometry (FCM) is a rapid, objective, reproducible method of making a quantitative assessment of cellular deoxyribonucleic acid (DNA) content (DNA-ploidy status) and the proliferative potential of neoplastic cells expressed as the fraction of cells in the flow S-phase fraction (SPF) of the cell cycle. The amount of DNA per cell can be used to indicate the cell position in the cell cycle. Normal cells have high genetic stability, and have a consistent chromosomal make up. Many cells exhibit an abnormal pattern with respect to chromosomal karyotype. Genetic changes in the cell genome may be small or large depending on the degree or stage of abnormality induced. In this study we analysed DNA-ploidy status, and S-phase fraction in 87 (71 papillary and 16 follicular) thyroid cancer. Regional meta had 46/87 (52, 8%) patients. Formalin fixed, paraffin embedded, tissue blocks from thyroid cancer was formed the material available for analysis. Aneuploidy was detected in 6/87 (5, 7%) patients (2/71 ; 2, 8% papillary and 4/16 ; 25% follicular), Aneuploid DNA content was found in 66, 6% patients with meta in neck. S-phase fraction (2, 86 vs. 4, 10 p=0, 018) was significantly decreased in papillary cancer. Patient with meta had higher (3, 01 vs. 4, 26 p=0, 021) S-phase fraction compared to the patients without meta. Flow cytometry DNA-analysis is commonly used to study tumor biology with the aim of predicting its behavior. Our results suggest that DNA-aneuploid, and high SPF tumours tend to be more aggressive clinical behavior.