The photochemistry of the NO/Ag(111) system has been studied by time-of-flight, photon-induced desorption and temperature-programmed desorption measurements. It is shown that two species are photoactive for NO desorption, one of which had previously been thought photoinactive. The time-of-flight (TOF) data show that NO is desorbed from both sites by a photochemical mechanism. This allows the previously unassigned high-temperature desorption of NO detected in temperature-programmed desorption to be assigned to a new form of adsorbed NO. In addition, the temperature-programmed desorption measurements show that there: are a range of inter-adsorbate interactions on the surface. Hence, the surface should not be thought of as comprising a range of non-interacting adsorbates.