The benthic communities of the soft seabed inside and outside the Cesano-Senigallia artificial reef (central Adriatic Sea) were investigated seasonally for 2 years (spring 1997 to winter 1999) to evaluate the effects of the reef on the surrounding bottom. The community living close to the reef is typical for the coastal area. Mean species richness and densities over the entire sampling period were comparable inside and outside the reef, while higher values were recorded at the control site. However, the ShannonWiener diversity index was higher close to the reef than at the control. Physical factors associated with the presence of the artificial structures appear to affect composition and abundance of the infauna community more than biological factors do (predation). The area inside the reef was characterized by fine mud favouring the settlement of deposit and suspension feeders, mainly polychaetes. Outside the reef, molluscs were numerically dominant, with an increasing proportion of sandy-bottom species with increasing distance from the structures. These differences were more marked in spring and autumn, while in the other seasons the reef effect appeared to be reduced to a narrow area close to the structures.