Telomerase is a ribonucleoprotein enzyme that maintains telomere length and confers immortality to ~85-90% of human cancers. Human telomerase is known to be present at telomeres throughout S phase¹ and to elongate telomeres following bulk telomere replication², but the mechanistic of cell cycle regulation of telomerase recruitment to telomeres in human cells is unknown. The budding and fission yeast homologues of the DNA damage-response protein ATM are critical for telomerase recruitment^3,4, but the involvement of ATM in telomerase recruitment to telomeres has not been demonstrated in human cells. The telomere-binding protein TRF1 has been shown to be phosphorylated at Serine 367 by ATM, leading to telomere elongation⁵. We therefore directly tested the hypothesis that ATM mediates telomerase recruitment to the telomere via phosphorylation of TRF1. Using hTR/telomere fluorescence in situ hybridisation, we demonstrated that ATM depletion or kinase inhibition resulted in decreased telomerase recruitment across the cell cycle, while TRF1 knockdown abrogated the removal of telomerase from telomeres in G2 phase. Depletion of TRF1 partially rescued the phenotype of diminished telomerase recruitment resulting from ATM knockdown alone, demonstrating that these two proteins act in the same pathway. Phosphomimetic mutation of TRF1 S367 showed reduced telomere localisation across the cell cycle, and resulted in increased telomerase at the telomere in G2 phase, while phospho-null mutation of TRF1 S367 was able to localise to telomeres and block telomerase access in S phase. The data support a model in which ATM phosphorylation of TRF1 at S367 is necessary for depletion of TRF1 from telomeres during S phase, and this in turn allows telomerase to access the telomere at the appropriate phase of the cell cycle to counteract replication-dependent telomere shortening. Furthermore, these data suggest that human telomeres trigger a DNA damage-dependent response during S phase that is important for their maintenance by telomerase and telomere length homeostasis. Steps in the ATM pathway of telomerase recruitment may be amenable to cancer therapeutic.