OBJECTIVE To determine whether failure to achieve pregnancy after repeated ET after ovum donation was due to an endometrial defect or to the embryo quality. METHODS Retrospective data analysis. METHODS A private infertility center. METHODS Four hundred sixty-seven donors (513 cycles) undergoing IVF donating oocytes to 266 recipients (423 cycles). METHODS Hormonal endometrial preparation with increasing dosages of valerate E2 (2,4, and 6 mg) and 100 mg of P. METHODS Pregnancy rates (PRs) and abortion rates in patients undergoing one to seven ETs after ovum donation. RESULTS Pregnancy rates in recipients that had one or two ETs were significantly higher (34.8%) compared with those of recipients having three or more ETs (15.1%). Abortion rates were significantly higher (54.5%) in recipients repeating more than three ETs than in the recipients having one or two ETs (29.1%). CONCLUSIONS Recipients that had failed to establish a pregnancy after two ETs had a lower PR in successive attempts, possibly because of a defect of their endometrial lining.