What is the prevalence of chronic endometritis (CE) in women with repeated unexplained implantation failure (RIF) at IVF, and how does antibiotic treatment affect the reproductive outcome? Chronic endometritis, associated with infection with common bacteria or mycoplasma, is common in women complaining of RIF and antibiotic treatment significantly improves the reproductive outcome at a subsequent IVF cycle. We have reported that CE is a frequent finding in women with repeated pregnancy loss and a significantly higher rate of successful pregnancies was achieved after adequate antibiotic treatment. Moreover, CE was identified in 30.3% of patients with repeated implantation failure at IVF and women diagnosed with CE had lower implantation rates (11.5%) after IVF cycles. In contrast, other authors reported that the clinical implication of CE should be considered minimal and that the reproductive outcome at IVF/ICSI cycles was not negatively affected by CE. A retrospective study was performed from January 2009 through June 2012 on 106 women with unexplained infertility and a history of RIF. All patients underwent hysteroscopy and endometrial sampling for histology and microbiological investigations. Women diagnosed with CE underwent antibiotic treatment and the effect of treatment was confirmed by hysteroscopy with biopsy. Within 6 months after treatment all women had a further IVF attempt. The IVF outcomes were compared in women without signs of CE (Group 1) and persistent CE (Group 2) after antibiotic treatment. Clinical pregnancy rate (PR), and live birth rate (LBR) were compared at post-treatment IVF attempt. Seventy (66.0%) women were diagnosed with CE at hysteroscopy. In 61 (57.5%) CE was confirmed by histology and 48 (45.0%) by cultures. Common bacteria and mycoplasma were the most prevalent agents. In 46 (75.4%) out of 61 women, with diagnosis of CE at hysteroscopy and histology, examinations were normal after appropriate antibiotic treatment control (Group 1) while in 15 (24.6%) cases signs of CE were still present (Group 2). At IVF attempt after treatment, a significantly higher PR and LBR was reported in women from Group 1 compared with women from Group 2 (65.2 versus 33.0% P = 0.039; 60.8 versus 13.3%, P = 0.02, respectively). Possible biases related to retrospective studies and to preferential referral of patients with CE, and limited number of cases. A prospective randomized clinical trial is needed to confirm our findings but in women with RIF a hysteroscopic evaluation of the uterine cavity to exclude CE should be considered and appropriate antibiotic treatment should be given before submitting the patient to a further IVF attempt. This research was funded by the University personal research grants of Ettore Cicinelli. The authors have no competing interests to declare.