In the 17 years up to 1979 189 kidneys have had an extended pyelolithotomy for staghorn calculus and have been followed up. In only 1 of 96 unilateral cases did a stone form in a normal contralateral kidney, whatever the outcome of surgery on the affected side. Seven early nephrectomies were performed for non-function and in 6 bilateral cases, with advanced renal failure, surgery did not arrest the loss of renal function. Regrowth of stone occurred in 43 cases (complete staghorns in 24). Regrowth did not occur in 18 of 20 incompletely cleared kidneys nor in 22 of 41 with persistent infection. Renal function was improved in 13 of 15 cases where it had not already deteriorated beyond a critical point. It is concluded that unilateral staghorn stones may be treated in their own right, without fear of compromising a normal contralateral kidney; that regrowth of stones is not inevitable, even with incomplete clearance; and that renal function is usually improved by surgery.