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If the crystals that form the stones remain tiny enough, they can pass through without even being noticed.

More men tend to develop stones than women, but the number of women who get kidney stones has been increasing. Whites are more prone to kidney stones than are African Americans, Hispanics, and Asians. The prevalence of kidney stones rises dramatically as men enter their 40s and continues to rise into their 70s. For women, the prevalence of kidney stones peaks in their 50s. Kidney stones also tend to run in families. Once a person gets more than one stone, he or she is more likely to develop others.

The most common type of stone contains calcium plus either oxalate or phosphate. These chemicals are part of a person's normal diet and make up important parts of the body, such as bones and muscles.

Kidney disorders such as malformations or blockages, and metabolic disorders such as hyperparathyroidism are also linked to stone formation. Genes also play a role. Also, more than 7 in 10 people with a rare hereditary disease called renal tubular acidosis develop kidney stones.

The pain often begins suddenly, when a stone moves in the urinary tract, causing irritation or blockage. Typically, a person feels a sharp, cramping pain the back and side in the area of the kidney or in the lower abdomen. Sometimes nausea and vomiting occur with this pain. Later, the pain may spread to the groin. Change of position doesn't improve the pain.

Fortunately, most stones can be treated without surgery. Most kidney stones can pass through the urinary system with plenty of water (2 to 3 quarts a day) to help move the stone along. In most cases, you can stay home during this process, taking pain medicine as needed. Your healthcare provider will probably ask you to save the passed stone(s) for testing. Other minimally invasive methods are available to treat stones. Surgery is only rarely needed.

If you have stones that develop again and again, you should try to drink enough liquids—water is best—throughout the day to make at least 2 quarts of urine in every 24-hour period.

Extracorporeal shockwave lithotripsy (ESWL) is the most often used surgical procedure to treat kidney stones. ESWL uses shockwaves that are created outside of the body to travel through the skin and body tissues until the waves hit the dense stones. The stones become sand-like and are easily passed through the urinary tract in the urine.