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The last glacial-interglacial transition (ca. 18–11 ka) was interrupted by abrupt climate events that differed in each hemisphere. During the Antarctic Cold Reversal (ca. 14.5–12.9 ka), the Southern Hemisphere high and mid latitudes cooled, while the Northern Hemisphere warmed. The pattern of change then reversed during the Younger Dryas (ca. 12.9–11.7 ka), which was characterized by cold conditions in much of the Northern Hemisphere. Well-dated paleoclimate records serve to reveal the possible mechanisms for these events. Here we present a reconstruction of the late glacial fluctuations of Quelccaya Ice Cap, located in the southern tropics, based on 38 new radiocarbon ages. Quelccaya was retreating from its Last Glacial Maximum (ca. 21 ka) extent by ca. 17.2 ka, and was located upvalley from its late glacial moraines by 13.6–12.8 ka. Quelccaya experienced a significant readvance that culminated at 12.5–12.4 ka, and then receded several kilometers to near, or within, its late Holocene extent by ca. 11.6 ka. This record provides the most detailed evidence yet of glacier fluctuations in the southern tropics during late glacial time.