Photometry of a large field around the young globular cluster Palomar 12 has revealed the main sequence of a low surface brightness stellar system. This main sequence is indicative of a stellar population that varies significantly in metallicity and/or age but in the mean is more metal-poor than Pal 12. Under different assumptions for the properties of this population, we find distances from the Sun in the range 17-24 kpc, which encompasses the distance to Pal 12, 19.0+/-0.9 kpc. The stellar system is also detected in a field 2° north of Pal 12, which indicates it has a minimum diameter of ~0.9 kpc. The orbit of Pal 12, the color-magnitude diagram of the stellar system, their positions on the sky, and their distances suggest that they are debris from the tidal disruption of the Sagittarius dwarf spheroidal galaxy. We discuss briefly the implications for the evolution of Sgr and the Galactic halo.