A most unusual family with aggressive Paget's disease is reported. Three brothers out of 10 siblings developed the disease at a relatively early age. Two of these brothers developed an osteosarcoma and died. It is emphasized that very little information is available concerning the predisposition to severe polyostotic disease and even sarcomatous change when Paget's disease begins at a young age or is familial. Possibly the risk of these serious complications is then greater than when the disease is sporadic and begins later in life.