A 23-year-old, male patient previously operated on four times for a recurring, benign, paranasal mass was admitted to our clinic with pain and swelling under the knee. Physical and radiological examination revealed a malignant process. The histopathological examination of the fine-needle biopsy specimen of the tibia was a malignant mixed tumor. Then, en-bloc resection, free fibular grafting, and fixation with blade plate was performed for one-third of the tibia, conserving the knee joint. Recurrences and metastasis were not observed after surgery and radiotherapy.