Monitoring for amnesic shellfish poisons (ASP) in wild and cultivated molluscs from Scottish waters commenced in 1998, following the of introduction of revised legislation from the European Community. The principle toxic compound, domoic acid (DA), was detected in a range of species and in some instances at concentrations above the regulatory limit. Although some harvesting closures were implemented in 1998, ASP caused much greater problems the following year. In 1999, the majority of scallop (Pecten maximus) fisheries from the Scottish west coast were closed due to ASP, resulting in considerable media attention and speculation on the role of nutrient inputs from local aquaculture. This paper will present data summarising the principal features of the 1999 toxic event. Although it is not possible to unambiguously identify the cause of such an event, the aim of this paper is to objectively summarise available information relating to the 1999 Scottish west coast outbreak, and to document the event as fully as possible.