Long interspersed nuclear elements (LINE-1) are well known as retrotransposons. A number of reports indicate that down-regulation of LINE-1 substantially affects growth of malignant cells and epithelial mesenchymal transition, which is difficult to be explained by its function as retrotransposon. More recent data indicate that LINE-1 is broadly involved in the regulation of telomere maintenance. This explains the essential role of LINE-1 for survival of malignant cells and further supports a global function of active LINE-1 elements in cell proliferation. We further discuss the implications of LINE-1-associated telomere regulation on evolution of telomeric structures, on embryogenesis and on therapy of malignancies.