Advanced endometriosis is often associated with ovarian endometriotic cysts, known as endometriomas. The cysts contain decomposed menstrual blood that looks like melted chocolate – hence the name “chocolate cysts.” They are space occupying cystic lesions within the ovarian connective tissue (stroma/theca) and if sizable (>1cm) often will activate the surrounding tissue to produce excessive amounts of male hormones (androgens) such as testosterone and androstenedione that can compromise egg development in the affected ovary (ies). This in turn often will result in egg numerical chromosomal abnormalities (aneuploidy) and reduced egg/embryo “competency”. Thus it is my opinion that any ovarian endometriomas larger than 1cm in diameter, should be removed eliminated before embarking on IVF. Aside from compromising egg quality in the involved ovary, endometriomas can also cause severe and intractable pelvic pain, heavy menstruation (menometrorrhagia) and painful intercourse. They can also rupture leading to dissemination throughout the abdominal-pelvic cavity.  Accordingly, they are best addressed sooner rather than later. Surgical Treatment: Conventional treatment of endometriomas involves complete surgical removal, usually conducted laparoscopically. Unfortunately, with surgery normal ovarian tissue can inadvertently be removed/damaged and result in scarring that that can compromise subsequent egg development in the affected ovary. Since many women who have endometriomas have already undergone previous surgery (ies) for endometriosis. Both the surgery (ies) and the advanced endometriosis will often have resulted in significant scarring and adhesion formation that can compromise subsequent visualization of, and access to anatomic structures during surgery, thereby increasing the risk of surgical complications. As such, many women with recurrent ovarian endometriomas are uncomfortable with the prospect of repeat surgery and its avoidance is often a factor in their decision to proceed with IVF. Sclerotherapy: About 15 years ago I reported on a new, safe and highly effective outpatient approach to treating endometriomas in women planning to undergo IVF. This treatment, referred to as sclerotherapy, involves ultrasound needle guided aspiration of the chocolate-colored liquid content of the endometriotic cyst, followed by the injection of 5% tetracycline hydrochloride into the cyst cavity. In more than 75% of cases, this will result in disappearance of the lesion within 6-8 weeks. In some cases the injection of tetracycline into the endometrioma causes a reaction that results in clear or blood stained fluid collecting in the original cyst cavity where the endometrioma had been. Upon re-aspirating the fluid in the seroma, the lesion will usually disappear permanently. In a small number of cases, the endometrioma comes back and sclerotherapy must be repeated or surgical removal undertaken. Ovarian sclerotherapy can be performed under local anesthesia or under conscious sedation. It has the advantage of being an ambulatory in-office procedure, low cost, and has a low incidence of significant post-procedural pain or complications as well as the avoidance of the need for invasive surgery. As such, sclerotherapy is in my opinion, the preferred treatment of endometriomas in women contemplating IVF and thus wish to preserve as much ovarian function as possible. It is a safe, effective and relatively inexpensive alternative to surgery. Since the procedure is associated with a small, but yet realistic possibility of pelvic adhesion formation; its use should in my opinion be confined to cases where IVF is the only treatment available to the patient or for women who intend to try and conceive through fertilization in their fallopian tubes (e.g. following natural conception or intrauterine insemination), who in my opinion would be better off undergoing laparotomy or laparoscopy for the treatment of their endometriomas.