The results of the operative treatment of 21 large longitudinal nephrotomies on account of the existence of cast calculi of the renal calyx are reported and discussed. In complete cast calculi with participation of the whole renal pelvis and all renal calyces this operation method leads to satisfactory results. Of the 12 cases (57-1%) with ideal postoperative morphological findings 83-3% became bacteriologically sterile; according to our opinion the lesion of the parenchyma due to operation is to be accounted for. In stone formations which do not fill all the calyces and yet in many cases in literature are called cast calculi, a pyelotomy or resection of the renal pole may by all means be the therapy of choice.