The concept of service life of structures is included in international standards ISO, in the European document EN 1990, in the recent document CEN for assessment of existing structures – Technical Specification TS and related prEN 1990 (part 2). The submitted contribution includes the definition of service life (performance time) tser, considering the resistance (resilience) of a structure R(t) and the effect of actions S(t). Due to the random variability of the variables R(t) and S(t), the service life tser, needs to be linked with probability that structural performance is partly or completely insufficient. Basically, serviceability and ultimate limit states, SLS and ULS respectively, should be considered. In the case of new concrete structures, a proxy limit state corresponding to the initiation of the degradation process (corrosion of reinforcement) is often considered (ILS). The application of the probabilistic approach is illustrated by a practical example of assessing the service life of a concrete industrial chimney. It appears that the predicted service life considerably depends on an adopted target reliability level. Optimum target levels for the ILS, SLS and ULS for a particular type of structures should be specified on the basis of economic optimisation studies.