Ollier's disease is a rare disease characterized by constitutional bone dysplasia with multiple enchondromas. The combination of haemangioma and chondromatoses is known as Maffucci's syndrome. Malignant degeneration of bone dysplasia into chondrosarcoma is a well-known complication, but a lesion of the base of the skull is exceptional. It is a slowly growing low-grade malignant tumour. Three new cases of chondrosarcoma of the base of the skull occurring in one patient with Marfucci's syndrome and two patients with Ollier's disease are reported and these cases are discussed in the light of the literature. A multidisciplinary approach, comprising surgery and radiotherapy, achieved good results.