In the paper an analytical model for the seismic risk assessment of historical buildings is presented. The seismic risk level is estimated through a seismic safety index, defined as the ratio between the capacity of the structure, herein evaluated through linear and nonlinear kinematic analyses, and the seismic demand, calculated according to the Italian building code prescriptions. Particular attention is paid to the verification method proposed by the Italian building code, underlying some aspects and criticalities. In the paper typical cases of overturning masonry walls characterized by load-bearing masonry structure are analyzed. Parametric studies are carried out on the portion of overturning wall analyzed by changing and combining basis hypotheses and conditions associated to common structural features not always ascertainable with simple qualitative tests and investigations. The effects of such type of uncertainties on the results obtained in terms of structural capacity are investigated and general trends of the seismic safety indexes are determined. The great variability of the results obtained by changing the basis hypotheses and the type of analysis is further investigated. In particular it is underlined the scatter in the results obtained by carrying out linear or non linear kinematic analysis. The wrong assessment of the seismic risk level can lead to misinterpretation of the type of intervention to do on the structure for the increase of its safety level and therefore to damages to its artistic-historic value.