A field study of landslides has shown that certain types of mass movement in the Mackenzie Valley, N.W.T. are associated with shear failure in frozen soil. These land-slides have been classified on a descriptive basis as being block and multiple retrogressive slides. A detailed description of the characteristic morphology, and of the soil and permafrost conditions at these slides has been presented.Quantitative analysis of slides at a site on the Mountain River are consistent with the view that failure occurs through frozen soil with the base of the slide in unfrozen clay. It appears that high pore water pressures control the available shear strength in the unfrozen clay and that the long term strength of the permafrost soils is governed by a frictional resistance.