Normal human somatic cells are diploid. But sometimes certain tissues of the human body contain elevated numbers of tetraploid cells. This tetraploid cell population seems to represent the first step of an ongoing process of polyploidization. All tissues containing tetraploid cells have in common the fact that they are subjected to stress, which is caused by a variety of circumstances like inflammation, elevated metabolism, ageing, repair processes or selection pressure. Tetraploid cells are supposed to play a beneficial role in these stress situations, because they are known to be more resistant in general and because they are characterized by an elevated biosynthetic activity. In contrast to their beneficial character, they have a big potential concerning the malignant development of a tissue: they play a crucial role in early morphological stages of the pathway hyperplasia-metaplasia-dysplasia-carcinoma. This report links several intracellular mechanisms with each other, which potentially determine the real fate of tetraploid cells.