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A kidney stone is a solid piece of material that forms in a kidney. Kidney stones may be the size of sand or gravel, as large as a pearl, or even larger. A stone can block the flow of urine and cause great pain.

Kidney pain
A kidney stone is a solid piece of material that forms in a kidney. Kidney stones may be the size of sand or gravel, as large as a pearl, or even larger. A stone can block the flow of urine and cause great pain.
Last reviewed July 4, 2022 by Kelly L. Stratton, MD, FACS, Associate Professor, Department of Urology, University of Oklahoma Health Sciences Center, Oklahoma City, OK. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team..