Why do stones form? Oxidative stress was the main topic of conversation at the American Urological Association meeting in Washington DC last week. Investigators from Valhalla NY reported that oxidative stress may facilitate calcium oxalate crystal formation. In turn, calcium oxalate crystals exerts more oxidative stress on renal tubular cells leading to more crystal formation. Investigators from Winston-Salem identified a new pathway for oxalate formation that is driven by oxidative stress. Investigators from Iowa City reported that high intake of the antioxidants alpha-carotene, beta-carotene and beta-cryptoxanthin lowered the risk of stone formation.