The symptoms of kidney stones vary depending on the size of the stones and whether they cause obstruction. If the stones are relatively small, they can usually pass smoothly through the ureters and urethra and be expelled from the body without causing any symptoms. When the stones are expelled, small stones can be seen in the urine. If the kidney stones are relatively large but do not cause obstruction in the kidneys or bladder, they generally do not cause any symptoms. Symptoms occur only when larger stones move downward and become lodged in the ureters, causing back pain, nausea, and vomiting. The stones can scratch the walls of the ureters, leading to blood in the urine. When stones get stuck in the urethra, it can cause painful urination discomfort and perineal pain. Since the stones can scratch the inner walls of the urethra, they may also cause blood in the urine.