Liposarcoma accounts for 11.5% of malignant tumors arising in soft tissues and is one of the most frequent types, but its occurrence in the head and neck region is rare. Dedifferentiated liposarcoma is one of the histological subtypes of liposarcoma, consisting of a mixture of an adipocyte-rich well differentiated component and a spindle cell-rich dedifferentiated component. Herein, we present a rare case of dedifferentiated liposarcoma arising in the neck. A 79-year-old man with a lump in his right neck was referred to our hospital after a biopsy at the previous hospital revealed a suspected spindle cell tumor. He underwent resection of the malignant tumor in the right neck and was diagnosed with a dedifferentiated liposarcoma.Postoperative radiation therapy of 70Gy was administered. No local recurrence or metastatic disease has been detected during a 16-month follow-up. This disease should be considered as one of the differential diagnoses when a soft tissue tumor is suspected.