The Geological Survey of Norway has detected >250 unstable rock slopes with significant postglacial deformation in Norway. Many of these could lead to catastrophic consequences through direct rockslide/rock-avalanche impacts and subsequent triggering of displacement waves upon impacting fjords or lakes. A hazard—and risk-classification system has been developed in order to prioritise follow-up activities at these sites, including more detailed investigations, periodic displacement measurements, continuous monitoring, and early-warning systems. This study presents a pragmatic methodology for assessing consequences of unstable rock slopes in Norway. The assessment comprises four steps: 1) volume estimation; 2) run-out assessment based on the volume-dependent angle of reach; 3) assessment of displacement wave propagation and run-up using empirical relations and generally applicable equations from physical model tests; and 4) estimation of the number of potential casualties.