Medical treatment designed to prevent stone formation is important in idiopathic calcium oxalate nephrolithiasis, because of the high rate of stone recurrence. Several randomized trials have established the values of conservative and drug treatments. A high fluid intake alone has been reported to inhibit the recurrence of stone formation in single stone formers. In patients with recurrent disease, a significant reduction in stone formation rate from pretreatment was found in the placebo group maintained on a conservative program, underscoring the importance of increased fluid intake and dietary modification. In patients with active recurrent stone disease, treatment with drugs along with a conservative program is necessary. Allopurinol, thiazide, potassium citrate and potassium-magnesium citrate have been shown to inhibit stone formation compared with placebo. It has not been clearly established that a selective treatment is more effective than a more randomly chosen drug treatment. Another advantage of medical approach is its ability to correct nonrenal complications of stone disease, such as bone loss that sometimes accompanies stone disease.