Endometriosis is the presence of endometrial glands and stroma outside the uterine cavity and uterine musculature. While ectopic endometrial implants are most often located in the pelvis, they can occur anywhere in the body. Chronic pelvic pain is typically defined as 3-6 months of pain, and has a prevalence of 3.8% in women aged 15 to 73. Endometriosis is the most common pathologic condition in adolescents with chronic pelvic pain, and has been reported in 25-38% of adolescents with chronic pelvic pain. The prevalence of endometriosis among adolescents undergoing laparoscopy for pelvic pain refractory to medical therapy has been reported to be 50-70%. Our experience with rates of diagnosis of endometriosis at the time of laparoscopy suggest that with the visual acuity afforded by advances in laparoscopic technology, and a surgeon experienced in intraoperative identification of endometriosis lesions, the prevalence may be even higher. In this chapter, we hope to raise awareness of the typical presentation of endometriosis in adolescents, provide health care providers with a straightforward diagnostic and therapeutic approach, and in so doing, facilitate early diagnosis and intervention. Early diagnosis and intervention are critical in ameliorating the long-term effects of endometriosis (pain and suffering, masses and infertility), reducing economic burden from long-term advanced disease, and improving affected young women’s quality of life.