Widespread till sheets, glacial lake and glacial-marine sediments on Banks, Victoria, and Melville islands, and on the Beaufort Sea Coastal Plain of the Canadian mainland, may record a late Pleistocene glacial advance which extended to the area as early as the Sangamonian (broad sense) to early Wisconsinan. These sediments overlie beds of interglacial character and underlie in places nonglacial deposits, which have provided both nonfinite and finite ages, and glacial sediments of unquestionable late Wisconsinan age. In other places only a single till sheet is observed between the last interglacial and Holocene sediment suites. Although some workers have argued that the glacial units mentioned above are all late Wisconsinan, stratigraphic, paleoecologic, and chronologic data ( 14 C, Th/U, and amino acid analyses), from several localities, indicate that the glacial sediments are of likely Sangamonian (broad sense) to early Wisconsinan age and that the nonglacial beds underlying or overlying these date respectively from the Sangamonian and middle Wisconsinan. The dispersal centre during the ice advance was situated, as during other advances in northwestern Canada, west of Hudson Bay. The ice generally extended further during the Sangamonian (broad sense)/early Wisconsinan than the late Wisconsinan but not as far as it did during the early and middle Pleistocene. To help resolve apparent incongruities in interpretation of the late Pleistocene deposits and ice limits it is postulated that extensive Keewatin Sector Ice of the Laurentide Ice Sheet may have first advanced in northwestern Canada during the Sangamonian (broad sense)/early Wisconsinan and remained there until it finally disappeared in the late Wisconsinan.