Telomeres are the physical ends of linear chromosomes and have an important role in protection of genomic integrity. Telomeres can be elongated by a unique ribonucleoprotein enzyme called telomerase. Telomere length maintenance is implicated in aging as well as the human diseases cancer and dyskeratosis congenita. In yeast, Est1p is known to co-mediate telomerase access and is essential for telomere length maintenance in vivo. This study characterizes a murine homologue of Est1, mEst1A. Murine embryonic stem cells with one disrupted mEst1A allele were generated, but viable null lines were not, suggesting possible lethality in the homozygous state. mEst1A mRNA was detected in most tissues examined, but not protein, perhaps due to low expression levels or inadequate antibodies. Immunoprecipitation analysis revealed an in vitro interaction of HA-tagged mEst1A with telomerase activity. These studies provide a valuable system with which to study further the role of Est1A in mammalian telomere length homeostasis.