Telomeres are specialized structures at the ends of chromosomes that prevent fusion events and promote chromosomal end replication. Telomeres are maintained by the regulation of telomerase activity and their capping by telomeric proteins. In the November Genes and Development, Hsu et al. show that the DNA repair protein Ku plays a role in telomere capping (Gene Dev 2000, 14:2807-2812). Hsu et al. used surface plasma resonance and co-immunoprecipitation to demonstrate that Ku forms a high-affinity interaction with the mammalian telomere binding protein TRF1. The Ku-TRF1 complex binds to telomeric DNA repeats. Furthermore, Ku80-deficient fibroblasts contained high levels of telomere fusions. These results suggest that Ku is localized to telomeres via its interaction with TRF1 and plays a critical role in preventing chromosomal end joining.