In November 2002 the Prestige tanker spilled 59 000 tonnes of oil off Galicia (north-west Spain) and contaminated a vast coastal area extending from northern Portugal to Brittany (France). Two study areas, a coastal lagoon (1 sample point) and a stretch of rocky coast (includes 5 sample points), were selected to examine changes on the diet of otters Lutra lutra L. before and after the oil spill. Diet was assessed from 1103 spraints, 553 collected in 2000, before the spill and 550 in 2003, after the spill. In the coastal lagoon, after spill, spraints contained more shrimp (Palaemon sp.), more prey of marine origin, and fewer gobies (Pomatoschistus sp.) and eels Anguilla anguilla. A decline of the eel population in the coastal lagoon may have caused otters to make more frequent visits to the sea. On the rocky coast, spraints contained more blennids in 1 of the 5 sampling points, however, the seasonal patterns of the principal prey species (Blennidae, Gadidae and Labridae) were similar across the 2 years of study. The differences may be attributed to common interannual variations in the diet of marine otters, but the design of this study cannot assess the degree of natural variation in the diet of coastal otters before the oil spill.