The debate on hydrosalpinx and impaired IVF outcome has mainly focused on the best treatment before IVF and on functional surgery as an alternative treatment. We would like to initiate a debate on the possible reasons why the outcome is impaired. We know that salpingectomy is effective in terms of improved birth rates after IVF, but we do not know exactly why. The main focus is on embryotoxic properties of the hydrosalpinx fluid, which include micro-organisms, endotoxins, cytokines, oxidative stress and lack of nutrients. The endometrial receptivity may be reduced as an effect of disturbed expression of the cytokine cascade, which is essential for implantation. The presence of excessive fluid in the uterine cavity may also be a mechanical hindrance to implantation. We believe that the hydrosalpinx fluid is of crucial importance, but the actual mechanism of action needs to be clarified.