Most kidney stones do not require surgery. The majority of stones, particularly those smaller than 5 millimeters, pass on their own with fluids and pain management. About 76% of stones in the 2 to 4 mm range pass spontaneously, and even stones up to 7 mm still have a 60% chance of passing without any procedure. Surgery becomes necessary when a stone is too large to pass, causes an infection, blocks urine flow, or triggers pain that medications can’t control.
When Stones Pass on Their Own
Your body can handle most small stones without medical intervention. The spontaneous passage rate drops steadily as stones get bigger: 87% for stones around 1 mm, 76% for 2 to 4 mm stones, 60% for 5 to 7 mm stones, 48% for 7 to 9 mm stones, and just 25% for stones larger than 9 mm. Location matters too. Stones closer to the bladder are more likely to pass than those still high in the ureter near the kidney.
Passing a stone typically involves drinking plenty of water, managing pain with anti-inflammatory medications, and waiting. A medication originally designed to relax the prostate can also help. It relaxes the smooth muscle in the ureter, widening the passage for the stone. In one study of stones between 4 and 10 mm, patients taking this medication passed their stones 90% of the time compared to 71% with fluids and pain relief alone. The process can take anywhere from a few days to four weeks.
Signs That Surgery May Be Necessary
Certain situations shift the decision from watchful waiting to active treatment. Both the European and American urology guidelines agree on the main triggers: stones that are unlikely to pass based on their size, persistent pain despite medication, obstruction that reduces kidney function, and infection behind a blocked stone. That last scenario, where bacteria are trapped behind a stone blocking urine flow, is the most urgent. It can lead to sepsis and requires emergency drainage before the stone itself is even addressed.
Seek immediate care if you experience pain so severe you can’t sit still or find a comfortable position, pain combined with fever and chills, nausea and vomiting that won’t stop, blood in your urine, or difficulty urinating. Fever with a kidney stone is especially concerning because it suggests infection, which can become dangerous quickly.
Shock Wave Lithotripsy
The least invasive surgical option uses focused sound waves from outside the body to break a stone into smaller fragments that can then pass naturally. It works best on stones that are moderate in size and not too hard. Stone density, measured on a CT scan, is one of the strongest predictors of success. Softer stones (below 1000 Hounsfield units on the scan) have an 88% clearance rate, while harder, denser stones drop to about 56%. Overall, the procedure succeeds in roughly 79% of cases.
Shock wave lithotripsy is typically done as an outpatient procedure. It’s most effective for stones in the kidney or upper ureter that are smaller than 20 mm. For stones in the lower part of the kidney, success rates are lower, and other approaches often work better. Larger stones may need multiple treatment sessions and carry a higher risk of fragment buildup in the ureter afterward.
Ureteroscopy
For stones stuck in the ureter, ureteroscopy is often the first-line approach. A thin, flexible scope is passed through the bladder and up the ureter to reach the stone, where a laser breaks it apart. No incisions are involved. Compared to shock wave lithotripsy, ureteroscopy produces higher stone-free rates within four weeks for ureteral stones, though the difference evens out by three months.
Recovery from ureteroscopy is relatively quick but comes with a catch: most patients get a temporary stent placed in the ureter to keep it open while swelling goes down. The stent typically stays in for about 8 days, though it can remain for weeks in some cases. Stent-related discomfort is common. About 60% of patients report that the stent affects their daily activities, and roughly a third experience bladder irritation symptoms like urgency and frequency. Pain from the procedure itself tends to peak the day after surgery and approaches normal levels around day five, but urinary symptoms often persist until the stent is removed.
Percutaneous Nephrolithotomy
For large kidney stones over 20 mm, or complex branching stones called staghorn calculi, a more involved procedure is the standard of care. Percutaneous nephrolithotomy involves making a small incision in the back and passing instruments directly into the kidney to break up and remove the stone. It’s the only approach with success rates that hold up regardless of stone size, which is why it’s the go-to for the biggest and most complex cases.
This procedure typically requires a hospital stay and a longer recovery period than the other options. Guidelines also recommend it as an alternative for mid-sized stones between 10 and 20 mm when other methods have failed or when the stone sits in a difficult location, like the lower pole of the kidney. For staghorn stones that fill multiple branches of the kidney’s collecting system, it offers the highest clearance rates of any single procedure.
Choosing the Right Approach
The treatment decision depends on a handful of practical factors: the stone’s size, where it’s located, how dense it appears on CT, and whether it’s causing complications like infection or obstruction. A 6 mm stone in the lower ureter might be managed with medication and time. The same stone lodged in the upper ureter with worsening pain might call for ureteroscopy. A 25 mm stone in the kidney almost certainly needs percutaneous removal.
Your own anatomy and health matter too. People with a single functioning kidney or stones blocking both sides need faster intervention because there’s no backup kidney filtering waste while you wait. Prior surgical history, body size, and bleeding disorders can also influence which procedure is safest.
Recurrence After Treatment
Whether your stone passes naturally or requires a procedure, the underlying tendency to form stones doesn’t go away with treatment. About 11% of people form another stone within two years, 20% within five years, and 31% within ten years. By the 15-year mark, nearly 4 in 10 people have had a recurrence.
The most effective way to reduce that risk is increasing your daily fluid intake enough to produce at least 2.5 liters of urine per day. Depending on the type of stone you formed, dietary changes like reducing sodium, moderating animal protein, and getting adequate calcium from food (not supplements) can also help. A 24-hour urine collection after your first stone event can identify specific chemical imbalances that guide more targeted prevention.