The role of telomerase in actively proliferating cells is assumed to be restricted to maintaining of telomeres above a minimum-length threshold, thereby preventing telomere exhaustion and chromosomal instability. However, forced telomerase expression in cells and mice with normal-length telomeres has shown that telomerase promotes growth and survival in a manner that is uncoupled from net telomere lengthening. These findings imply that telomerase might have a fundamental role in tumour growth and survival, even at stages when telomeres are sufficiently long.