We report two cases of femoral nerve palsy after radical prostatectomy due to compression ascribed to the use of a ring retractor. The first case is in a 69-year-old man who fell when getting out of bed on the first postoperative day. Physical examination revealed hypoesthesia around the patella and weakness of the quadriceps muscle. The second case is in a 66-year-old man who complained of numbness of the anteromedial aspects of the right thigh and inability to extend his right knee on the first postoperative day. Postoperative femoral nerve palsy is not a well-recognized complication in urology. The literature was reviewed and the management of postoperative femoral nerve palsy was discussed.