GOMOS (Global Ozone Monitoring by Occultation of Stars) on Envisat measures ozone, NO2, NO3, H2O, aerosols, neutral air density, and temperature in the stratosphere and mesosphere by detecting the absorption of starlight in UV, visible and infrared wavelengths. During bright limb conditions GOMOS also observes scattered solar radiation. GOMOS will deliver ozone concentration profiles at altitudes 15-100 km with a vertical resolution of about 1.5 km and with a global coverage. As a self-calibrating method stellar occultation measurements provide a basis for a long-term monitoring of ozone profiles. We will present results achieved during the first year of the GOMOS validation program. The validation is based on comparisons with Mars, ozone sondes, balloon borne instruments, other satellites as well as with climatological and meteorological data.