Severe osteolysis is a rare complication of lymphangioma. It can progress despite treatment and may be fatal. Four patients presented with massive osteolysis and serious related complications. Of these, two responded well to OK-432 therapy with arrest of the osteolysis. Complete recovery from life-threatening pleural effusion has been noted in one. Of the two nonresponders, one died of progressive osteolysis of the cervical and occipital bones, the other, despite therapy, still shows progressive osteolysis of the left leg from the femur to the phalanges. A boneless leg may be the outcome.