Context: Isthmocele is a reservoir-like pouch defect on the anterior wall of uterine isthmus and is related with previous cesarean section scar. A clear association was demonstrated between isthmocele and secondary infertilty. Objective:To evaluate the effect of GnRH agonist pretreatment in patients with isthmocele before frozen thawed embryo transfer cycles. Methods: Retrospective case series Patients: Patients with isthmocele and secondary infertility Interventions: Patients received three cycles of GnRH agonist (Leuprolide Acetate- Lucrin Depot 3.75 Abbot Turkey) pretreatment before frozen thawed embryo transfer. Main Outcome Measures: Volume of isthmocele, pregnancy rate, clinical pregnancy rate, and live birth rate Results: Retrospective data of 8 patients with isthmocele and secondary infertility were evaluated. In all cases the volume of isthmocele decreased after GnRH agonist treatment. Mean volüme of isthmocele was 377 mm3 and 44.1 mm3 before and after treatment with GnRH agonist respectively. 2 of the cases (25%) became pregnant after frozen thawed embryo transfer and these two patients delivered healthy babies. Conclusions: GnRH agonist pretreatment seems to be effective to reduce the isthmocele volüme before in vitro fertilizatipn cycles . However clinical pregnancy rates does not seem to be improved. Further studies are needed about the subject.