Four siblings with tumoral calcinosis and hyperphosphatemia have been studied for several years. In one the disease was recognized prior to its clinical appearance because of hyperphosphatemia. The hyperphosphatemia is not a result of renal insufficiency or of an abnormal parathyroid response. The hyperphosphatemia and tumors did not occur independently in our patients, and serum phosphorus determinations may be useful for screening. Recurrence after total excision of a mass is common and should be treated by early re-excision. The initial results of this treatment have been fairly good.