Kidney stones develop in supersaturated urine. The supersaturation is the driving force for a phase change from a dissolved salt to a solid or crystal. Nephrolithiasis is very common in Western societies and a substantial source of morbidity and cost. Various patient and environmental factors have been identified. In the United States, the lifetime risk is estimated to exceed 8%. There are five major types of urinary stones: calcium oxalate, calcium phosphate, struvite, uric acid, and cystine. Most stones are composed of calcium oxalate or a mixture of phosphate (85%) as such stones are radiopaque on plain abdominal film. Struvite stones are typically caused by increased production of ammonia secondary to infection with urease-producing organisms, such as Proteus or Klebsiella.