Past survey work in the Isles of Scilly has shown the area to be of high biological and conservation interest because of the variety of habitats and species present. This survey was carried out in order to obtain more information about subtidal sediments and communities, especially from sites not previously examined, and to enable some clarification of habitat and community distributions. Fieldwork took place in September 1988. Work was completed at 15 sites, which were well spaced around the archipelago. A team of divers used an airlift suction sampler to obtain sea bed samples for biological analysis and also took core samples for sediment particle size analysis. Habitat features were recorded in situ. In the laboratory, animals from each sample were identified and data recorded in tabular form. Sediment particle size analyses were carried out by a combination of dry sieving techniques and the use of a Malvern 2600 laser particle sizer. Descriptions of each site were prepared based on the data obtained. Similarity between sites was found to be very low. The number of taxa found in samples showed wide variation. Although in some cases, population distributions appeared to be strongly linked to sediment characteristics, some taxa were apparently randomly distributed throughout the survey area. On coarse sediments, distinct divisions into community types were inappropriate. However, the composition of benthic communities within fine sediments showed less variation, and species present were more predictable. Some of the shallow subtidal areas are rich and potentially vulnerable. It would be useful to have more regular data from specific sites within these areas. The Isles of Scilly sediments are of high nature conservation importance. The habitat overall has a number of unique features which result in the communities present being different and interesting. In addition, the area is almost entirely unspoilt by human activities at the present time.