All over the world, including in Poland and Portugal, there are exist steel structures that are 100 or more years old. In particular, the construction of railway lines in the 19th and 20th centuries contributed to thousands of steel structures for bridges and viaducts being constructed. Knowledge of materials used in the past and their properties, after many years of use, is now necessary to determine the usefulness of the constructed structures. The authors of the abstract intend to present their own experience in this field. Among other things, they want to present the results of experimental research involving a 100-year-old bridge from the point of view of fatigue-related crack growth in puddle iron. The paper presents the results of tests on historic bridge steel from structures operated in Poland and Portugal. One of the most important issues related to the safety assessment of this type of bridge is the assessment of resistance to fatigue crack propagation. The paper presents the results of tests – fatigue crack kinetics curves determined in accordance with ASTM E647. In addition, a comparative analysis and assessment of the impact of microstructural degradation processes on fatigue life was performed. Furthermore, for selected cases, the issue of R-factor influence was discussed, i.e. an analysis was performed using original mathematical models as well as the concept of effective DK, which takes into account the effect of fatigue crack closure. An important aspect from a serviceability point of view is also the procedure of extending the fatigue life of cracked bridge steel components. The authors conducted experimental tests using various techniques to arrest crack growth (stop hole, CFRP strips in various combinations). As a result, the advantages and disadvantages of each of these solutions were compared and discussed.