Cystic angiomatosis of bone is a rare disorder characterized by widespread lytic bone lesions with or without associated soft tissue or visceral lymphangiomatosis. The disorder is often initially incorrectly diagnosed as Langerhans cell histiocytosis. Unfortunately, biopsy of long bone lesions will often yield only fluid, thereby making a histologic diagnosis difficult. This report describes the MR findings in a patient with cystic angiomatosis of bone. We believe that the MR findings are highly suggestive of the correct diagnosis and that MR should eliminate the need for excisional biopsy in future cases.