The aetiology of endometriosis is poorly understood resulting in a number of different models of pathogenesis. None of these models completely explains all of the available evidence. As such, there remains significant uncertainty about the origins and development of the disease, and in particular the involvement of the lymphatic system in that process. A 37-year-old patient with known endometriosis presented with a rapidly growing endometrioma following previous surgical drainage. The cyst enlarged over 5 months to extend above the umbilicus, necessitating a mid-line laparotomy and right salpingo-oophorectomy for the relief of severe pain symptoms. At the time of surgery, significant retroperitoneal inflammation and fibrosis were noted and a 2.5 cm pelvic lymph node was excised. This contained a cystic structure that was concluded to be an endometriotic cyst within the lymph node. The clinical significance of this is unknown but it does highlight the role the lymphatic system may play in the pathogenesis of endometriosis.