The Gorham-Stout Syndrome (Gorham's massive osteolysis) is a rare condition in which spontaneous, progressive resorption of bone occurs. The aetiology is poorly understood. We report six cases of the condition and present evidence that osteolysis is due to an increased number of stimulated osteoclasts. This suggests that early potent antiresorptive therapy such as with calcitonin or bisphosphonates may prevent local progressive osteolysis.