Summary. Antarctic krill is a key species in the Antarctic food web, an important prey item for marine predators and a commercial fishery resource. Although single-beam echo-sounders are commonly used to survey the species, multi-beam echo-sounders may be more efficient because they sample a larger volume of water. However, multi-beam echo-sounders may miss animals because they involve lower energy densities. We adapt distance sampling theory to deal with this and to estimate krill density and biomass from a multi-beam echo-sounder survey. The method provides a general means for estimating density and biomass from multi-beam echo-sounder data.