Deposits from the proglacial lake Grøndalsvatn in the vicinity of Ålfotbreen, the westernmost glacier in southern Norway, show evidence of avalanches that descended in to the lake between at least 2910 ± 60 and 2590 ± 60 14C yr BP ( 1170-770 cal. BC). A possible short glacial period from 2590 ± 60 to 2140 ± 60 14C yr BP (330-60 cal. BC) is thought to be represented by a thin, grey silt interlayer. After this date, the inflow of glacial meltwater to the lake ceased, indicating that few or no glaciers existed on the Ålfotbreen plateau at that time. A drop in organic-matter content and an associated increase in clastic-material supply at the core depth of 100 cm may indicate some renewed glacial activity in the lake's catchment from about 1650 ± 60 14C yr BP (cal. AD 370-450). The textural and carbon-content change at about 60 cm depth indicates an increased Neoglacial activity in the catchment from 910 ± 70 14C yr BP (cal. AD 1030-1220). The winter snow-mass balance is the most important factor controlling the net mass balance of Ålfotbreen.