The Comacchio Lagoon is a wetland complex remaining after the reclamation of a large area for agriculture purposes. It has been managed during last centuries for fishing and extensive rearing of euryhaline fish and salt extraction. Now it covers some 120 km2 and it consists of four main major districts. In two of these (composed of 18 sectors) we have studied the change of the abundance and of the trophic structure of the waterbird community occurred between 1996-1999 and 2002-2003, employing the following 15 guilds: Swimming ichthyophagous, Wading ichthyophagous, Flying ichthyophagous, Omnivores, Swimming invertebratophagous, Flying invertebratophagous, Probers, Peckers, Scythers, Malacophagous, Predators of ground animals, Raptors, Dabbling phytophagous, Diving poliphagous and Dabbling poliphagous taking into account their abundance both by number and biomass. The abundance of the entire community has dropped by more than 50%. All the significantly varied guilds dropped their abundance (Swimming ichthyophagous, Swimming invetebratophagous, Diving poliphagous and Dabbling poliphagous) except two, only one of which quite abundant (Scythers), which have significantly increased, at least in one district. The composition of the waterbird community has varied significantly in one district and in the entire area, where some increase of the diversity occurred too. As a consequence of the different variation of the abundance of the guilds, the composition of the community has varied also in most sectors and the arrangement of the similarity among them varied between the two periods.