The scope of the paper is to present the development and application of a new procedure for the seismic risk assessment at urban or territorial scale of unreinforced masonry buildings (URMB). The procedure, named MeBaSe, is based on four main features: the formulation of the structural capacity and response in terms of mechanics concepts, the representation of seismic demand and structural capacity by means of displacement, the inclusion of the most commonly acknowledged sources of uncertainty and the consideration of in-plane and out-of-plane failure mechanisms. The procedure aims to the evaluation of seismic risk of classes of buildings and is intended as a tool that could in perspective solve most of the drawbacks associated with existing procedures. The uncertainty originating in the material properties and the structural response is treated separately from that coming from the statistics of the population of buildings. The former is directly included in the computation of probability of failure of a class of buildings, whilst the latter is considered in a second stage. The demand, represented by a displacement response spectrum, can be obtained from regional probabilistic seismic hazard studies, and is defined by the median, for each spectral period, and by the corresponding scatter. Concerning the limit states, appropriate median values corresponding to each given drift limit state are used, depending on the type and quality of masonry. For the out-of-plane mechanism, the procedure is restricted so far to simple oneway bending mechanisms. A case study for the validation of the procedure has been carried out in the city of Benevento, Italy, and some preliminary results are presented in the paper, showing the feasibility of the new methodology.