We report a case of systemic intraosseous lipomatosis involving the proximal femur, both ends of the tibia, and the tarsal and metatarsal bones. The lesions progressed during a five-year follow-up with a pathological fracture of the tibial plateau. CT scans were characteristic and helpful in diagnosis but MR imaging added little information. Intraosseous lipomatosis is a hamartomatous malformation due to hyperplasia of adipose tissue, and is fundamentally different from solitary benign intraosseous lipoma. Management involves reconstruction of any pathological fracture. Large progressive lesions should be treated by curettage and grafting in an attempt to prevent such fractures.