SummaryIt was the aim of the study to develop a new surgical method to repair the so called rectovestibulum fistula (RVF) in the horse: In this context it was intended to combine and take up advantageous aspects of methods already established in plastic surgery for this traumatically caused defect. Known disadvantages of the different methods such as surgical transfer of the fistula to a third degree perineal laceration, difficult practicability and high incidence of recidives were minimized. The primary aspect of the new surgical method is the surgical transfer and inclusion of a second degree perineal laceration by which main parts of the perineal body and shincter ani in toto are maintained. After training phases for general feasability of the new procedure surgery was simulated on isolated pelvic organs (n = 15) and in straight before sacrified animals (n= 8) the operations were performed on 6 experimental and 4 client mares. The healing process until the removal of the sutures was without any clinical complications. On the average the clinical healing of the fistula operated was completed after two weeks. Complications such as intestinal constipation, tenesmus, excessive inflammatory reactions or general worsening of well-being of the mares did not show up in any case. In 8 of 10 cases the fistula was completely closed after a first surgery. In two (experimental mares) of the 10 cases there was a recidive of a now considerable smaller fistula which was in one mare closed and healed after a second surgery. In one of these two mares a second recidive occured demanding a third surgery session. Ultrasound measurements revealed a remarkable increase of the interrectovestibular tissue. After euthanasia of the experimental mares pathologicalanatomical and histological examinations of the rectal bottom and vestibulum roof within the area of the surgical site revealed similar results in all samples prooving a definite healing with scars which has to be regarded as stable. As a conclusion it can be stated that the new established plastic surgery of RVF can be recommended for practical use as it fulfilled the main aims of (1) durable and stable surgical closure of the RVF, (2) maintenance of integrity of the closing function of the anal sphincter, and (3) reliable external genital closure. Keywords:mare, rectovaginal fistula, plastic surgery, perineal integrity