Objective: Abdominal scar endometriosis is a recognized condition that has been described following a wide variety of gynaecological procedures. We report a case of endometrioma, presenting as a painful subumbilical swelling, mimicking an incarcerated incisional hernia. Clinical Presentation: A 35-year-old woman presented with a painful subumbilical swelling that had been present for 6 months, but had increased in size and become more painful the day prior to admission. Her past medical history included four caesarean sections. Physical examination revealed a firm, tender and irreducible subumbilical nodule with no cough impulses, mimicking a small incarcerated incisional hernia. Intervention: Exploratory laparotomy through the same lower midline incision revealed a subcutaneous swelling resembling an organized chocolate cyst of endometriosis. Apart from intra-abdominal adhesions, no connection to intra-abdominal structures was identified. Histopathology of the specimen was consistent with abdominal scar endometriosis. Conclusion: Endometrioma was diagnosed in this 35-year-old woman following histological examination of a specimen removed during laparotomy. It is recommended that endometrioma should be considered in the differential diagnosis of subcutaneous, scar-related hernias and various abdominal wall masses following gynaecological operations.