Assessing urban slope stability requires consideration of significant uncertainties including those associated with shear strength and pore water pressure. For site-specific studies, there is considerable merit in adopting a reliability approach within a probabilistic framework based on widely accepted geotechnical models. Regional slope stability studies are facilitated by using a GIS-based approach. Considerable effort is required to prepare regional data sets including topography and geology and to develop a landslide inventory. Reference is made to a comprehensive knowledge-based approach for assessing failure susceptibility and hazard within an urban region in Australia. Each hazard zone is associated with an estimated likelihood of failure. In this paper the corresponding reliability index for each zone is estimated based on the assumption of a normal distribution. Estimates of the mean safety factor associated with each hazard zone under different assumptions of coefficient of variation and pore water pressure ratio are also made.