The renal function before and after operation and histological findings were studied on 16 kidneys of 16 cases with staghorn calculi and similar renal stones, which were subjected to nephrolithotomy, extended pyelolithotomy, and extended pyelolithotomy plus nephrolithoyomy without clamping renal vessels.From the results of the postoperative segmental renal function (GFR, RPF, urinaly volume, Fishberg, renogram and IVP) and histological findings, the following conclusions were obtained.1) The gross appearance of the operated kidneys, presenting the preoperative renogram of obstruactive and delayed pattern, was normal. Histologically, the cellular infiltration in the stoma and increase of the connective tissue were hardly recognized. After operation, Fishberg showed lower values, but GFR and RPF were normal.2) The gross appearance of the operated kidneys with the preoperative renogram of hypofunctional pattern, was almost normal. Histologically, the cellular infiltration in the stoma and increase of the connective tissue were observed.Fishberg, GFR and RPF after operation were low, but urinary volume was within normal limit.3) The gross appearance of the operated kidneys with the preoperative renogram of non-functional pattern showed remarkably uneven shapes. Histologically, there were seen the cellular infiltration in the stoma, increase of the connective tissue and moreover, arteriosclerosis. Fishberg, GFR and RPF after operation were low, and excretion of urine was inhibited.From the results mentioned above, the author is of the opinion that the kidney having the preoperative renogram of non-functional pattern should be severed if the function of the contral ateral nonoperated kidney is normal.