Id2 plays a key role in epithelial cells regulating differentiation, cell cycle and proliferation. As human skin constantly renew itself and is the first target of irradiation, it is of primary interest to evaluate whether such a gene may be regulated in keratinocytes exposed to ionizing radiations. We show here that Id2 is induced in response to gamma irradiation and have investigated the consequence of this regulation on cell fate. Using RNA interference, we observed that Id2 extinction significantly reduces cell growth in human keratinocytes through the control of the G1/S transition of the cell cycle. We have investigated whether Id2's impact on the cell cycle may have a physiological role on the cell's ability to cope with radiative stress. Indeed, when Id2 is down regulated through interfering RNA, cells are more sensitive to irradiation. Conversely, when Id2 is over expressed, this somehow protects the cell. We propose that Id2 favors reentering the cell cycle after radio-induced cell cycle arrest to permit the recovery of keratinocytes exposed to ionizing radiations.