To assess the biological effects of the Prestige oil spill (November 2002) on coastal ecosystems, mussels (Mytilus galloprovincialis) were sampled in 22 locations along the coast of Galicia and the Bay of Biscay in April, July and September 2003 and in February, April, July and October 2004. Several cell and tissue-level biomarkers were measured in digestive gland. Flesh condition index and gamete development stages were assessed as supporting parameters. AOX activity, a marker of exposure to peroxisome proliferating compounds including PAHs, was particularly low in Galicia in 2003 and further was markedly increased in several localities in 2004. Values of the labilization period (LP) of the lysosomal membrane were low in all the studied localities, especially in Galicia in 2003. In 2004, LP values raised, evidencing a certain recovery in mussel's health. In agreement, the volume density of basophilic cells was markedly high in 2003 and showed a decreasing trend throughout 2004. Parameters defining the structure of digestive alveoli showed few variations between 2003 and 2004. Significant correlations between several biomarkers and total polycyclic aromatic hydrocarbons (PAHs) were found. In conclusion, employed biomarkers detected highest degree of disturbance in areas most impacted by the oil spill (Galicia) and were able to evidence a recovery trend during 2004, related to a decrease in total PAH concentrations in mussels.