Most urinary tract stones occur in the upper urinary tract. Their composition varies widely depending upon metabolic alterations, geography and presence of infection. Their size varies from gravel to staghorn calculi. Some are the result of inborn errors of metabolism - gout, cystinuria, primary hyperoxaluria. Most are radio-opaque.

Although some renal stones remain asymptomatic, most will at some time result in pain.

Small stones arising in the kidney are more likely to pass into the ureter where they may cause severe colicky pain; large stones may be asymptomatic because of their immobility.

Superimposed infection may result from mucosal trauma and/or obstruction.