Masses within the inguinal region have multiple differentials, with hernia recurrence being the main concern after surgical hernia repair. We present an unusual case of an inguinal mass after hernia repair, which after much investigation, was revealed to be a seeded endometrioma. A 48-year-old female presented with a large mass growing in her left inguinal region. Her history was significant for only endometriosis, an open left inguinal hernia repair, a diagnostic laparoscopy, and laparoscopic cholecystectomy. Although the mass was initially suspected to be hernia or mesh related, the patient gave a history of a fluctuating change in size which correlated with her menstrual cycles. MRI and biopsy confirmed endometriosis, which was later surgically excised with a margin to prevent future recurrence. Benign soft tissue tumours such as endometriomas have the capacity to seed from the uterus or peritoneum into the abdominal wall. As this usually occurs after a caesarean section, it was not initially a differential for our inguinal mass. Although sometimes unavoidable, this also highlights the importance of keeping the hernial sac intact particularly if the patient has a history of endometriosis.