We report evidence for cascading of shelf-edge water down the continental slope northwest of Ireland at 55N in February 1996. The measured surface density contrast between shelf-edge and slope waters was 0.01 kg m-3 and the resulting dense plume was 20-50 m thick over the continental slope and penetrated to a depth of 500 m. Cascade waters were warmer but saltier than overlying slope waters and their shelf-edge origin was confirmed by relatively higher chlorophyll concentrations and a distinctive nutrient signature. Other cross-slope transects 100 km north and south of the cascade site showed dense water at the shelf edge (a situation assumed to be favorable for cascading) but no deep downslope penetration of shelf water. A one-and-a-half layer dynamical model indicates that the observed downslope penetration of the cascade can be accounted for by the measured excess density of shelf-edge waters even with a realistic level of entrainment of overlying slope waters.