Analysis of 56 cases of coralliform urolithiasis has shown, among other things, the normally poor symptomology. This is in contrast to the poor prognosis which, in the absence of treatment, almost always ends in the destruction of the kidney. Besides ten immediate nephrectomies, 52 conservative operations were performed on forty patients. These conservative operations are difficult, long and meticulous. They are greatly facilitated by using an endocavitary lighting source of cold light. The use of contact X-ray is indispensable. Removal of stones must be absolutely complete. The number and extent of the nephrotomies must be reduced to a strict minimum. One must avoid the big, destructive nephrotomies--except, perhaps, in children. With the help of all these precautions, the results are encouraging; no secondary nephrectomies until present time, only two real relapses, and three small previously-undetected calculi. Yet, thanks to the systemic use of the cold light and of the contact X-rays, there were no more "undetected" calculi for the last 4 1/2 years.