Immediate breast reconstruction is an important tool for patients to accept and overcome their breast cancer, as well as for cosmetic reasons. However, its use in patients who require postmastectomy radiation therapy (PMRT) is not yet clear. The purpose of this study was to analyze the effects of PMRT and reconstruction on each other. The time of initiation of PMRT, the prognosis, and the cosmetic results were investigated in patients who underwent immediate reconstruction using autologous tissue. In the case of delayed reconstruction using autologous tissue after PMRT, radiation damage of the chest skin, design of the flap, and cosmetic results were investigated. In 38 patients who underwent immediate reconstruction and PMRT between 2006 and 2015, 20 patients received neoadjuvant chemotherapy, and their mean time before starting PMRT was 9.7 weeks after surgery (range 7-18 weeks). Three patients underwent delayed PMRT (more than 12 weeks) due to partial flap necrosis and wound infection. Of 28 patients (2006-2010), 23 were disease free (stage I: 2/2, stage II: 15/16, stage III: 6/10), one patient (stage III) had distant metastases, and 4 patients died of primary disease (stage II: 1/16, stage III: 3/10). Unacceptable deformation of the reconstructed breast was observed in 4 patients who had partial fat necrosis of the grafted flap or skin necrosis of the mastectomy flap. In 20 patients who underwent delayed reconstruction between 2006 and 2015, 15 (75%) patients underwent replacement of irradiated chest skin with flap skin to reconstruct a soft and natural shape breast. The flap survival rate was 100%, and unacceptable deformation of the reconstructed breast was not seen. In the case of immediate reconstruction using autologous tissue, it is important to graft a flap with a good blood supply to avoid delaying PMRT and achieving a good cosmetic result, because flap necrosis or wound infection delays PMRT and causes scar contracture after PMRT. In the case of delayed reconstruction after PMRT, chest wall skin with radiation damage should be resected and replaced by flap skin.