The authors suggest a change in their surgical classification of renal calculi to conform the description to the new techniques in the treatment of renal calculosis. Category "C" describes the morphology and topography of renal stones in five degrees (C1-C5); small letters "p", "s", "m", "i" indicate the pelvis, superior, middle, inferior calyces; "n" and "a" symbolize a stone having a size similar to or exceeding normal shaped renal cavities. "Cu" indicates ureteral calculi; small letters, "l", "i", "p" indicate lumbar, iliac, pelvic ureteral stones. "N" describes the nature of the calculi. Category "E" stands for the excretory tract: "+" and "-" indicate the presence or absence of dilatation; the small letters "e", "i" show the extra or intrarenal position of renal cavities; "no" and "o" indicate absence or presence of intrinsic obstruction of the excretory tract. "R" points out the number of surgical recurrences. Category "P" indicates the function of the parenchyma; numbers 1, 2, 3 refer to normal renal function, moderate or serious insufficiency. "U" stands for unique functional or anatomical kidney; "I" indicates the presence of infection.