IntroductionLiposarcoma is the most common retroperitoneal soft tissue tumor. Liposarcomas are often asymptomatic and are discovered after they become huge. Surgical resection is the first‐line treatment for retroperitoneal liposarcoma, but the surrounding organs are often resected with the liposarcoma.Case presentationA man saw a hospital with a complaint of left lower abdominal distention, and a left retroperitoneal mass was noted on imaging examination. The patient was referred to our hospital. The mass extended from the retroperitoneum through the inguinal canal to the thigh and involved the femoral nerve and psoas major muscle. A well‐differentiated liposarcoma was suspected, and an open surgical resection was performed. Complete resection of a retroperitoneal liposarcoma extending to the thigh was achieved without postoperative complications.ConclusionTreatment strategies for huge retroperitoneal liposarcomas are important to balance antitumor efficacy and postoperative quality of life.