Endometriosis is the presence of endometrial tissue outside the uterus, most commonly found in the ovaries, pelvic peritoneum, and rectovaginal septum. The exact cause is unknown but theories include retrograde menstruation through the fallopian tubes. Symptoms include dysmenorrhea, dyspareunia, and infertility. Diagnosis involves clinical exam, ultrasound, MRI, and laparoscopy with biopsy. Treatment options include pain medications, hormonal therapy to induce pseudopregnancy or menopause, and surgery to remove lesions and adhesions. Combined medical and surgical approaches may provide the best outcomes.