The earthquake behaviour of a four-storey reinforced concrete (R/C) building, which was constructed in 1933, is investigated here, before and after a recent maintenance and retrofitting. The numerically predicted earthquake behaviour of the initial structure, under the provisions of the current Greek Seismic Code, demonstrated the low resistance of this building to the design seismic loads. The estimate of the strength of existing structural members was based on specific tests performed in-situ as well as at the Laboratory of Strength of Materials and Structures, Aristotle University. The retrofitting scheme included the strengthening of vertical structural elements by jacketing, as well as the use of carbon fibre reinforced plastics (CFRP) for the improvement of the bearing capacity of the slabs. The numerically predicted earthquake behaviour of the retrofitted structure demonstrated the sufficient resistance of the retrofitted building.