GNRH1 and endometriosis: <h4>Objective</h4>The objective of this study is to evaluate the effectiveness of prolonged GnRH agonist (GnRH-a) suppression combined with letrozole and intensive luteal phase support in a patient with severe adenomyosis undergoing frozen-thawed embryo transfer (FET).<h4>Design</h4>The study design was a case report.<h4>Setting</h4>The setting was a tertiary referral in vitro fertilization (IVF) clinic.<h4>Subjects</h4>The subject was a 41-year-old woman with a history of primary infertility with severe adenomyosis and endometriosis.