The potential environmental risks posed by Depleted Uranium (DU) weapons have been a widely debated issue. In autumn 2001, as a follow-up to its earlier work on DU in Kosovo, UNEP organized a scientific field mission to investigate the possible environmental consequences from DU used in Serbia and Montenegro during the military conflict of 1999. The mission investigated five targeted sites in Serbia, one in Montenegro and a targeted military vehicle. Field measurements were performed at each site, and 161 samples were collected for laboratory analyses. While the results of this study are consistent with previous findings in Kosovo, important new discoveries were made concerning penetrator corrosion, airborne DU particles, and risks for future groundwater contamination. Also, important lessons were learned from the decontamination measures conducted by Yugoslavian, Serbian and Montenegrin authorities. Given the remaining scientific uncertainties and adherence to the precautionary principle, UNEP recommends a series of measures to minimize risks and identifies important future research needs.