Kidney stones are hard masses that can grow from crystals forming within the kidneys. Doctors call kidney stones “renal calculi,” and the condition of having such stones “nephrolithiasis.”

Most kidney stones are made of calcium oxalate. People with a history of kidney stone formation should talk with their doctor to learn what type of stones they have—approximately one stone in three is made of something other than calcium oxalate and one in five contains little if any calcium in any form. Calcium oxalate stone formation is rare in primitive societies, suggesting that this condition is preventable.¹ People who have formed a calcium oxalate stone are at high risk of forming another kidney stone.

The information included in this article pertains to prevention of calcium oxalate kidney stone recurrence only—not to other kidney stones or to the treatment of acute disease. The term “kidney stone” will refer only to calcium oxalate stones. However, information regarding how natural substances affect urinary levels of calcium may also be important for people with a history of calcium phosphate stones.