Malignant transformation of synovial chondromatosis into chondrosarcoma is unusual. Thirteen cases and one series have been reported; only four of them developed in the hip. The overall survival is about 50%, possibly because of the difficulty of arriving at a correct early diagnosis (radiographically and histologically) and subsequent adequate surgical therapy. We report two patients (ages 30 and 50 years) in whom synovial chondrosarcoma developed in previously excised synovial chondromatosis of the hip. The diagnosis was made with modern imaging techniques (computed tomography and magnetic resonance imaging) and verified by open biopsy. The early recognition allowed a wide limb-saving resection; both patients are disease free 3 and 2 years after surgery.