A 72-year-old woman underwent complete deep inguinal lymph node dissection on her right side subsequent to metastasis from malignant melanoma. On the second postoperative day, the patient reported of nausea and vomiting. She presented with a mass in the resected area that gradually increased in size to approximately 15×20 cm. The wound was opened a few hours after onset of symptoms and a large femoral hernia with 40 cm of small intestine was immediately revealed protruding in the groin. Prophylactic suturing of the inguinal ligament and Coopers ligament can reduce the risk of postoperative femoral hernia. Further, the authors argue that drainage for seroma and haematoma should be performed with utmost care, considering other possible causes and, if necessary, guided by ultrasonography.