Endometriosis is a chronic disease affecting approximately 10% of women of reproductive age. It is strongly associated with pelvic pain and infertility. Women with advanced stages of the disease (stage III-IV) have markedly reduced fertility compared with the general population. A Swedish study has shown that about 22% of women undergoing treatments with assisted reproductive technologies (ART), such as in vitro fertilization (IVF), are affected by endometriosis. The optimal management of women with advanced endometriosis and infertility remains uncertain. Some clinicians advocate proceeding directly to IVF, while others suggest surgical removal of endometriosis lesions prior to IVF in order to improve the chances of pregnancy. Currently, evidence is limited to a small number of observational studies. Two observational studies and one meta-analysis have suggested that surgery before IVF in women with deep endometriosis may increase both pregnancy and live birth rates compared with IVF alone. However, no randomized controlled trial (RCT) has yet been conducted to answer this important clinical question. This study will be the first national multicenter randomized controlled trial to compare surgery followed by IVF with IVF alone in women with advanced endometriosis and infertility. All Swedish centers for highly specialized endometriosis surgery and fertility treatment will participate. Eligible participants are women under 39 years of age with stage III-IV endometriosis who seek fertility treatment. Participants will be randomized in a 1:1 ratio to one of two groups: * Surgery prior to IVF (laparoscopic excision of endometriosis lesions, followed by IVF). * Direct IVF without prior surgery. The primary outcome is the cumulative live birth rate within three years of randomization and initiation of the allocated treatment. Secondary outcomes include pregnancy rates, time to pregnancy, treatment-related complications, patient-reported quality of life, and cost-effectiveness. Our hypothesis is that surgery before IVF will lead to a higher cumulative live birth rate compared with IVF without prior surgery in women with advanced endometriosis. The results of this trial are expected to have significant impact on clinical practice and international guidelines. Regardless of outcome, the study will provide robust evidence to guide treatment strategies, improve the care of women with advanced endometriosis and infertility, and potentially reduce healthcare costs by identifying the most effective pathway to achieving pregnancy.