Aging is a multifactorial and highly complex process. Telomeres, repetitive DNA elements at the end of linear chromosomes, and telomerase, the reverse transcriptase responsible for the synthesis and elongation of telomeres, are implicated in mammalian aging. Intact telomeres are essential for genome stability and chromosomal integrity, as well as for extended proliferative life span of cells. Lack of telomerase activity in human somatic tissues and concomitant telomere erosion correlate with age-related pathologies. Mouse models either lacking or overexpressing telomerase support the notion that short telomeres cause premature aging. Recent evidence suggests that telomerase might have other functions besides maintaining telomere length. Here, we propose a possible role for telomerase in delaying the aging process, which is independent of telomere length. The positive effects of telomerase on aging seem to come of the price of tumour promotion. These antagonistic roles of telomerase in aging and cancer may have important implications for putative telomerase based therapies.