Communication: Corrosion in high-T(c) superconductors (HTSC) caused by water vapor is examined. HTSC thin films prepared using the laser ablation technique are shown to lose their superconducting properties due to the topotactic formation of a new hydroxylated phase which is a result of the corrosion. The mechanism of the corrosion process, which could be important in future applications of HTSC, is discussed.