The assemblages of blenniid fishes were studied by underwater visual methods at 15 rocky shore sites of the coast of Liguria (northern Italy) in 1998 and 10 sites along the Ligurian and Tyrrhenian Sea (west coast of Italy) in 1989 and 1990. A total of 12 species was found, with little variation in species composition among sites. Fish density ranged from 0.4 to 0.9 individuals/m2. Similarity among the sampling sites of Tyrrhenian Sea followed a geographical latitudinal gradient (north-south). The study at a smaller spatial scale in the Ligurian Sea showed that both geographical distance and environmental features influence the similarity among sites. The presence of Scartella cristata at 21 out of 25 sampling stations indicate that this species, which formerly did not occur in the northern Mediterranean, is now firmly established in the coastal waters of Italy. These findings provide additional evidence of a notable and rapid biological modification in coastal fish communities, probably related to temperature increase of the Mediterranean Sea.