Late Quaternary calderas have been identified at 12 of 40 volcanic centers in the eastern Aleutian arc, and sufficient radiocarbon dates and geologic information have now been obtained to either date or constrain the timing of the climactic caldera-forming eruptions. At least eight major caldera-forming events, each characterized by estimated eruption volumes of more than 10 km3, occurred at seven different volcanic centers in the Holocene, and as many as six of these had estimated eruption volumes of more than 50 km3. Eruptions of similar magnitude formed two other calderas in Wisconsin time. The dating of these hitherto little-known events adds significantly to the previously existing chronology of large prehistoric eruptions. This refined chronology is important in understanding eruption-induced climate changes, in assessing volcanic hazards, and in developing a tephrochronology for northwestern North America.