A region on the U.S. East Coast exhibiting sediment instability is present on the continental margin seaward of the coast of Delaware and the Baltimore Canyon Trough area. A detailed bathymetric and seismic-reflection survey of a 7.5 by 13.0-km area, together with box, hydroplastic, and piston cores, affords an integrated study of a large submarine slide with a volume of 11 cu km on the continental slope northeast of Wilmington Canyon. The geotechnical properties and sedimentologic characteristics of the seafloor show variations that are associated with the slide. The slump block is believed to be composed of Pleistocene sediment with sediment failure occurring on the slope along a late Tertiary erosion surface which formed the gross morphology of the continental margin. he suggested mechanism for triggering the sediment failure is increased wave energy associated with a lower stand of sea level during the late Pleistocene. Mass wasting of material downslope by creep is a process which apparently still is occurring.