Unlike hernias and neoplasms of any other body site, the sciatic hernia is uncommon and the finding of an atypical lipoma in it is probably unique. In such instance making the correct diagnosis is paramount in order to perform a procedure with a radical intent. A CT scan must be considered any time a rare form of hernia is observed and the surgical treatment of a retroperitoneal lipoma has to be radical, to prevent a recurrence. This is the strategy followed by the authors in a case of a 53 year old lady presenting with a large retroperitoneal lipomatous neoplasm within a sciatic hernia.