Durability of mid-twentieth-century precast prestressed concrete structures has become an issue in many countries. In the 50s and 60s of the last century, a large number of post-tensioned and pre-tensioned concrete structures (e.g. bridges, crane beams, roof girders) were constructed throughout Europe. Design guidelines as well as materials and technologies applied in those days were significantly different from current ones. The rules of factory production control and on-site supervision differed from the ones applied today. Currently, these structures achieve (or have already achieved) the design life period. Owners or managers of such structures face the dilemma of whether these objects can still be safely operated, or certain intervention is needed or perhaps - in extreme cases - demolition is necessary. The procedure for assessment of technical state of old prestressed structures is briefly described in the paper. Based on numerous research of existing structures in Poland (which are representative of many European countries), their weak spots, which may determine safety of the whole object, are shown. The paper also provides ways of analysing the behaviour of such structures, allowing for more accurate determination of their load bearing capacity.