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Radiocarbon dates and relative ages of soils on moraines provide evidence of a substantial late-Holocene (>2600 BP) readvance of glaciers in the western part of the arid Andes at 29 degrees S. The glacier in the Encierro valley, northern Chile, reached about 60% of its late-Pleistocene extent. The equilibrium line altitude ELA during this advance remained between 4250 and 4500 m which is above the modern 0 degrees C isotherm of the free atmosphere during summer. It is suggested that, given the specific climate at high elevations in the extremely arid Andes, a substantial increase in effective moisture is sufficient to explain this advance, whereas no significant temperature depression was needed. This compares favourably with the regional late-Holocene climatic history, when lake levels were higher and effective moisture greater than today between 3000 and 1800 BP. Judging from regional palaeodata, we suggest that this late-Holocene humid spell was most likely related to increased Westerly moisture sources from the Pacific.