This study provides evidence that the fish louse, Anilocra physodes has inhabited the Island of Gran Canaria in the Canary Archipelago and that it is the only island in the Archipelago that is infested. Underwater SCUBA visual surveys were conducted on the island of Gran Canaria during the summers of 1993 and 1998, and on the island of Lanzarote (180 km Northwest of Gran Canaria) during the summer of 1993 to characterize the distribution and infestation rates of A. physodes, found to parasitize the parrotfish Sparisoma cretense. Despite their sympatric distribution throughout the Mediterranean and northeast Atlantic and the broad specificity of A. physodes, this is the first documented occurrence of A. physodes on a fish of the family Scaridae. Of the 451 S. cretense observed on Gran Canaria in 1993, 13.1% were parasitized. On the other hand, no parasites were observed on the 637 parrotfish on Lanzarote. In 1998, of the 904 parrotfish observed on Gran Canaria, 11.5% were parasitized. The most likely factors for the absence of parasitic isopods on Lanzarote include lower host density, greater cleaner fish abundance, limited isopod dispersal, and human intervention