Abstract The work presented here investigates cladding residual stress (CRS) and its important in realistic (best-estimate) lifetime prediction for nuclear reactor pressure vessels. The analysis is based on a survey of previous investigations, on the authors' own specially performed measurements (on specimens, on a 1:5 scale PWR nozzle and on a 1:5 scale PWR vessel), and on analytical models for stress analysis, fracture mechanics and lifetime prediction. The measurements were made using the centre-hole, air-abrasive method. The stress analysis model was based on a fictitious temperature field (for the CRS simulation) and on the ADINA and BERSAFE finite element codes. The fracture mechanics analysis was performed according to the virtual crack extension method ( J- integral ), while the COVASTOL computer code was used for the probabilistic lifetime prediction. A high (250–400 MPa) CRS was determined, and its importance to the vessel integrity estimated quantitatively.