The thesis deals with the seismic performance assessment of an office building in Kranj. The design seismic forces of structural elements were estimated on the basis of the q-factor method, which is one of the possible methods to assess seismic resistance of the structure according to Eurocode 8-3. The design check was made so that all structural elements were verified by checking that seismic demands due to the reduced seismic action do not exceed the corresponding capacities. For calculation of the capacities, mean value properties of materials were used. In the fourth chapter the office building is described and the seismic demand is estimated for the selected structural elements. The structure was modelled by program Tower 7. Two structural models were made in order to investigate the effects of masonry infills. The seismic demand on the structural elements was compared to the design values of load carrying capacity. Such a comparison represents a basis for the evaluation of the seismic resistance using q-factor method. It is shown that the structure is not able to undertake the design seismic loads. However, the q-factor method provides very limited information, since it is based on the linear elastic analysis and verification of performance of each structural element without consideration of redistribution of seismic action due to structural damage. Thus the q-factor method cannot be used to provide information about the damage of the structure, which is a key information in the process of rehabilitation of a building. For this reason, it is more appropriate to assess seismic performance of existing buildings by using nonlinear analysis. Due to the lack of resources it is still difficult to perform such analysis by engineering practitioners.