A record of volcanic activity within the Vatnajökull ice cap has been obtained by combining data from three sources: tephrostratigraphic studies of two outlet glaciers, a 415-m-long ice core from northwestern Vatnajökull, and written records. The record extends back to a.d. 1200 and shows that the volcanic activity has a 130–140 yr period. Intervals of frequent eruptions with recurrence times of three to seven years alternate with intervals of similar duration having much lower eruption frequency. In comparison with other parts of the plate boundary in Iceland, eruption frequency is greater, episodes of unrest are longer, and intervals of low activity are shorter. The high eruption frequency may be the result of a more sustained supply of magma, owing to the area's location above the center of the Iceland mantle plume. When combined with historical data on eruptions and earthquakes, our data indicate that rifting-related activity in Iceland as a whole is periodic and broadly in phase with the volcanic activity within Vatnajökull.