The concept of seismic vulnerability is used to predict the average level of damage that can occur on a large scale in buildings under the action of a seismic shock of known intensity. The use of the concept of vulnerability is considered in the context of the particular typology of reinforced concrete buildings commonly found in northern Morocco and not having been the subject of a seismic design ensuring adequate protection. The vulnerability scale is adapted from the Italian method called "Gruppo Nazionale per la Difesa dai Terremoti" (GNDT), where a recalibration of the weighting coefficients is carried out in order to better fit the local architectural characteristics of the buildings. A correlation is then proposed between the damage index considered as the main effect sought and the causes formally schematized through the concept of vulnerability. The results of a field survey conducted after the strong earthquake of magnitude 6.3 that struck the northern region of Morocco in 2004 have shown that the proposed method allows to correctly assess the vulnerability.