The aim of this study was to compare the potential biological and clinical aggressiveness of familial vs sporadic papillary thyroid carcinoma (PTC), by assessing clinicopathological characteristics, survival parameters and DNA ploidy in two series of 107 patients, matched by age, gender, disease extension and follow-up duration. The results showed higher presence of tumour multifocality in familial PTC (index cases) and a trend to higher occurrence of extrathyroidal extension in the familial PTC subgroup with three or more affected elements.