Plain radiograph of the pelvis showing a large exophytic mass arising from the right iliac bone of a middle-aged man. He presented with gradually increasing swelling around his right upper thigh. This case is a secondary chondrosarcoma which arose from an osteochondroma. It shows the charactristic "rings and arcs" pattern of calcification. Case produced with permission, courtesy of Dr. Frank Gaillard. Radiopaedia. Complete case is here.