Of 250 cases of percutaneous nephrolithotomy perforation of the left colon has been observed in 2 men with mobile kidneys. The clinical signs were rectal hemorrhage with shock in 1 case and passage of gas through the nephrostomy tract in the other case. The perforation was not suspected during the nephrolithotomy. Both patients were treated surgically. In view of the risk of colonic perforation during percutaneous nephrolithotomy, great care should be taken during puncture. This risk is increased in cases with an excessively lateral tract or when the anatomical relationships are modified in subjects with mobile kidneys. Surgical repair is required when the perforation is intraperitoneal or when there is a risk of complications. Simple surveillance is only justified when the perforation is extraperitoneal and when there is no risk of complications.