R-flurbiprofen, a non cyclooxygenase inhibiting non-steroidal anti-inflammatory drug (NSAID), has been found to inhibit tumor growth in various animal models. In vitro experiments have shown that this effect is based on the induction of a cell cycle block and apoptosis. Cell cycle inhibition has been explained by activation of the c-Jun-N-terminal kinase (JNK) and downregulation of cyclin D1 expression. However, the molecular mechanism leading to apoptosis is unknown. Here, we show that treatment of the human colon carcinoma cell line HCT116 with different concentrations of R-flurbiprofen leads to an accumulation of p53 protein which is accompanied by an increase in phosphorylated p53 at serine 15. Mutation of serine 15 to alanine by site directed mutagenesis and overexpression of the mutated p53 gene in HCT116 cells, revealed that these cells are significantly less sensitive to apoptosis induced by R-flurbiprofen than pcDNA control cells, as measured by PARP-cleavage and flow cytometry. By contrast, no difference was detected between HCT116p53ser15ala cells and HCT116 pcDNA cells with respect to induction of a cell cycle block after R-flurbiprofen treatment. Moreover, in nude mice HCT116p53ser15ala overexpressing xenografts were significantly less sensitive to R-flurbiprofen than HCT116 pcDNA control xenografts. In conclusion, we were able to show that induction of apoptosis in HCT116 cells after R-flurbiprofen treatment is at least partly dependent on the tumor suppressor gene p53 and that mutation of p53 at serine 15 impairs the apoptotic potency of R-flurbiprofen.