The paper addresses the main uncertainties associated with the occurrence of rainfall induced landslides. Spatial variability of site conditions, local geology and rainfall contributes significantly to the uncertainty of landslide hazard. Urban landslide problems require the management of slopes of marginal stability. Assessment of hazard, vulnerability and risk require the use of observational approaches, the analysis of rainfall data and the relationship between rainfall magnitudes on the one hand and slope movement on the other. Details of research carried out in the Illawarra area of New South Wales, Australia are provided. Reference is made to the comprehensive database enabling the determination of landslide frequencies. The concept of antecedent rainfall percentage exceedence time (ARPET) is explained. The use of inferred threshold rainfall magnitudes for real-time prediction and warning is explained. Uncertainties concerned with this approach are explored with particular reference to rainfall distributions in the study area.