Pluripotency can be induced in somatic cells by overexpression of a set of transcription factors. The process has extremely low efficiency and slow kinetics. Here Utikal et al. show that cells with low endogenous p19Arf levels and immortal fibroblasts deficient for components of the Ink4a/Arf/p53 pathway yield iPS colonies with a threefold faster kinetics and at a significantly higher efficiency compared with wild-type cells, reaching frequencies of up to 100%. Genetic deletion of p53 in cellular subpopulations that normally fail to reprogram rescues their ability to produce iPS cells. Pluripotency can be induced in somatic cells by overexpression of a set of transcription factors, but the process has extremely low efficiency and slow kinetics. Here, cells with low endogenous p19Arf levels and immortal fibroblasts deficient for components of the Arf–Trp53 pathway yield induced pluripotent stem cell colonies with up to threefold faster kinetics and at a significantly higher efficiency than wild-type cells, reaching frequencies of up to 100%. The overexpression of defined transcription factors in somatic cells results in their reprogramming into induced pluripotent stem (iPS) cells1,2,3. The extremely low efficiency and slow kinetics of in vitro reprogramming suggest that further rare events are required to generate iPS cells. The nature and identity of these events, however, remain elusive. We noticed that the reprogramming potential of primary murine fibroblasts into iPS cells decreases after serial passaging and the concomitant onset of senescence. Consistent with the notion that loss of replicative potential provides a barrier for reprogramming, here we show that cells with low endogenous p19Arf (encoded by the Ink4a/Arf locus, also known as Cdkn2a locus) protein levels and immortal fibroblasts deficient in components of the Arf–Trp53 pathway yield iPS cell colonies with up to threefold faster kinetics and at a significantly higher efficiency than wild-type cells, endowing almost every somatic cell with the potential to form iPS cells. Notably, the acute genetic ablation of Trp53 (also known as p53) in cellular subpopulations that normally fail to reprogram rescues their ability to produce iPS cells. Our results show that the acquisition of immortality is a crucial and rate-limiting step towards the establishment of a pluripotent state in somatic cells and underscore the similarities between induced pluripotency and tumorigenesis.