Abstract: Normal human diploid fibroblasts (HDFs) exposed to a single H2O2 subcytotoxic stress display features of premature senescence, termed stress-induced premature senescence (SIPS). In this work, our aim was to study SIPS in Werner syndrome (WS) fibroblasts, derived from a patient with WS, a disease resembling accelerated aging. The subcytotoxic dose for WS fibroblasts was found to be inferior to that of normal HDFs, indicating WS fibroblasts are more sensitive to hydrogen peroxide than normal HDFs. SA β-gal activity has been shown to occur both in vitro and in vivo, and we studied the proportion of WS cells positive for SA β-gal. Intriguingly, the percentage of positive cells did not increase with the dose of H2O2 used. Contrary to other HDFs, the DNA-binding activity of p53 in WS fibroblasts did not increase in SIPS. We found, based on our results, that WS fibroblasts feature an altered stress response and do not reach SIPS from H2O2. We suggest that the proportion of cells that in normal HDFs would enter SIPS instead die in WS fibroblasts. Last, we propose that aging derives from a loss of integrity of the chromatin structure, which occurs faster in WS patients.