In the process of inspection of reinforced concrete structures being in long-term service, deflections of beams and slabs beyond the standard values are often detected, which is attributable to concrete creep occurring in the case of the early dismantling of shuttering. At the same time, any visual signs of their reduced load-bearing capacity are absent. Taking into account the high degree of uncertainty of the factors influencing the long-term strains of the concrete, the safe service life of such structures can vary within a rather wide range, and its actual value can be assessed only through probabilistic methods of the reliability theory. The paper presents the results of the investigation of the influence of concrete creep caused by the early dismantling of the shuttering on the reliability of prefabricated reinforced concrete floor beams of a three-storey building. The data obtained through the instrumental verification of the mechanical characteristics of the beam materials and their deformed state were used for design modelling. The authors carried out the probabilistic creep analysis of the beam through the method of statistical modelling taking into account the variability of concrete strength for various values of the relative humidity of the ambient air and the age of concrete at the moment of the load application. The statistical characteristics of the stress-strain modulus and the beam deflection values with various levels of probability were obtained. Due to con-crete creep, the safety analysis showed a 2,4 times reduction in the beam reliability index at the service life of a structure of 70 years.