We studied the fever attacks and their factors in the cases of percutaneous nephrolithotomy (PNL) and transurethral ureterolithotripsy (TUL). In PNL, fevers were significantly higher and more frequent in the cases with infected urinary stones than those with sterile stones, but prophylactic administration of antibiotics did not lower the fever or its frequency of attack. There was no significant difference between the cases of single procedure and those of multiple procedures although multiple procedures were likely to increase the frequency of fever attacks. In TUL, single J-catheter indwelling decreased fever attacks, but infection and administration of antibiotics did not affect the fever significantly. However, careful control of urinary tract infections before and after operation and of intrarenal pressure during operation are thought to be most important for prevention of fever attacks and urosepsis.