El Niño-Southern Oscillation (ENSO) is the largest source of inter-annual variability operating in the earth's climate system with enormous ecological, social, and economic impacts. As the instrumental record of ENSO variability is limited to the past 150 yr, the search for proxies sensitive to ENSO has become a priority task in recent years. It is vital to expand the sparse network of annually resolved and exactly dated ENSO-sensitive proxies to entirely capture the spatial variability of the ENSO coupled ocean-atmospheric phenomenon. Several tree-ring records have been used to reconstruct past ENSO variability, however, none of them are from tropical South America. The Polylepis tarapacana woodlands form the world's highest elevation treeline. Trees grow on the Altiplano plateau between 4000–5200 m elevation (16°–23° S). The climate variability in this climatically transitional tropical–subtropical region is strongly modulated by ENSO. Two chronologies of P. tarapacana along the Western Cordillera in the tropical central Andes were analyzed to determine the strength of the ENSO signal present in these tree-ring records. The growth of P. tarapacana has a strong common signal amongst trees in a single site and between sites across the Altiplano. Ring formation is induced by climatic conditions during the previous and current growing season (December–February), at the time of the strongest ENSO influences on the Peruvian Coast. Tree growth variations show opposite relationships with climate between consecutive growing seasons. During the current growing season, ring-width variations show positive and negative relationships with temperature and precipitation, respectively. Both tree-ring chronologies are significantly correlated with austral spring–summer (August–February) SST in the Niño3.4 region and show oscillatory modes within the classical ENSO bandwidth. Our results support the idea that P. tarapacana chronologies from the south-central tropical Andes provide high-resolution records extremely sensitive to ENSO in the tropical Pacific, and represent an important component to be considered in future multiproxy ENSO reconstructions.