Telomerase, a cellular ribonucleoprotein (RNP) reverse transcriptase, is not detected in most normal human tissues but is almost universally expressed in human cancers. Telomerase is transcriptionally silenced during human development, except for a subset of cells in highly proliferative tissues such as the germ line, blood, skin, and intestine. Even in these tissues telomeres progressively shorten with increased age. It has generally been thought that the exclusive function of telomerase was to prevent telomere shortening, but recently a number of reports have suggested a role for telomerase in addition to maintaining telomere length. Results indicate that, even in the absence of limiting telomere length, added telomerase still promotes tumorigenesis and cell proliferation. No specific mechanism by which telomerase might do this has been proposed. We think it is premature to ascribe nontelomere maintenance functions to telomerase. Various caveats exist and specific controls still need to be addressed.