The present study is the first report of a sanguinicolid infection affecting sea bream Sparus aurata cultured in net cages in the NE of Spain. The disease was associated with trickling mortalities during the cold season (1999 and 2000). Examination of gill wet mounts of the affected population revealed that sanguinicolid infection was present in 82.6 and 100% of the fish sampled in 1999 and 2000, respectively. Adult flukes, which were located in the kidney, were tentatively identified as members of the family Sanguinicolidae, subfamily Cardicolinae. Eggs and miracidia were found in the gill vascular structures. The inflammatory response triggered by the parasites was moderate and the lesions caused by either eggs and miracidia in the gills or adult flukes in the kidney were not extremely severe, possibly because of the moderate intensity of the parasitosis. Histological observations of sanguinicolid infected sea bream presented here are compared with those reported in other fish species. The role played on sea bream morbility and mortality by other factors (occurrence of a simultaneous moderate monogenean infection, immunological impairement related to low water temperatures) is discussed.