The interaction of HNCO with Rh(111) has been studied with reflection absorption infrared spectroscopy. HNCO adsorbs dissociatively on Rh(111) at 150 K to yield adsorbed H and NCO species. On clean Rh(111) the NCO species was found to decompose readily to adsorbed CO and N on warming to room temperature. Preadsorbed oxygen atoms result in an increase in the relative amount of NCO, shifts the dominant vibrational band of NCO from 2160 to 2182 cm(-1), and significantly stabilizes the NCO species on Rh(111). The possible relevance of the stabilization of NCO in the NO + CO reaction is discussed.