Waiting for the stone to pass on its own without intervention is called spontaneous passage. The rate of spontaneous passage is determined by the stone size and location. High rate of passage: stone less than 4 mm in size and located near the bladder. Low rate of passage: stone greater than 6 mm in size and located closer to the kidney.

During observation, pain medications are prescribed and the patient is instructed to drink a lot of water (more than 2 liters/day) and strain the urine to catch the stone if it passes. If the stone does not pass while on observation for 2-3 weeks, then intervention by lithotripsy or surgery is necessary.

Observation is not an option with a coexisting infection, severe pain not controlled with medications, intractable nausea and vomiting, and in patients with underlying kidney disease. These patients move directly to intervention by lithotripsy or sugery.