The incidence of stones in patients with enterocystoplasty is reported as 12-52.5%. Most patients will have multiple physical factors such as immobility, need for self catheterisation and poor urine drainage, so that it is not certain that an intestinal reservoir is the cause of stones on its own. There is little or no evidence that mucus is an aetiological factor. Foreign bodies in the reservoir, such as staples, increase the risk of stone formation from 13% to 43%. Stones require surgical removal. Minimally invasive techniques may be used for small stones. A low velocity disintegrator is required so that fragments are not propelled into the intestinal mucosa. Stones are infective in origin in 86% of cases, but 14% are sterile. Metabolic screen shows that 80% of patients have risk factors for at least three different types of stone. All patients have raised pH (mean 6.93) and hypocitraturia. Raised serum and urinary calcium, hyperoxaluria and hyperuricosuria are found in up to 33% of patients.