Necrosis of fatty bone marrow, caused by lipolytic enzymes, is a rare complication of several pancreatic disorders. A 44-year-old man with polyarthritis, subcutaneous nodules, and osteolysis associated with alcoholic pancreatitis underwent magnetic resonance (MR) imaging of the knees. In the marrow of the distal femur and proximal tibia, the images showed multiple foci of abnormal signal intensity compatible with the diagnosis of fat necrosis secondary to acute pancreatitis. Because MR imaging can depict abnormalities in fatty marrow that seem to precede necrosis, this modality may add early diagnostic information.