Do antidumping laws have anti-competitive consequences and restrict trade? These questions arise repeatedly in multilateral and bilateral trade talks. Although there are reasons to suspect that antidumping laws do have such effects, there is little known about the size of these effects in practice, and even less about the mechanism by which they occur. This paper provides estimates of the trade impacts of U.S. antidumping law and the determinants of suit filing activity from 1980-1985.