Chondro-osseous differentiation of three benign or malignant fat tissue tumors--two chondrolipomas and a liposarcoma with cartilaginous metaplasia--was studied with magnetic resonance (MR) imaging and compared with their pathological findings. The results suggest that demarcation of cartilage tissue can be clearly defined on MR imaging when the size of the cartilaginous area is large. Myxoid matrix, degenerative fat tissue and lipodystrophic change may decrease the delineation of the cartilage tissue.