The collection of fossil fishes from Monte Bolca (Eocene of Northern Italy), deposited at the Muséum national d'Histoire naturelle, Paris, was examined for the detection of parasites or traces of their activity. Of the 349 fishes studied, 62 showed a fairly well-preserved integument for the observation of skin nodules. Of these, all teleosts, six specimen exhibited skin nodules.The percentage of diseased fish is therefore 9.7%. The concerned species were Exellia (= Semiophorus) velifer (Volta, 1796), Abromasta (= Pagellus) microdon (Agassiz, 1839), Pseudosparnodus microstomus (Agassiz, 1839), Eozanclus brevirostris (Agassiz, 1833–1844) and Cyclopoma gigas Agassiz, 1833–1844. These pathologies of the integument are morphologically similar to those that can be observed in extant taxa. The causes of fish nodules are diverse (toxins, infectious agents, physical causes, imunological causes, nutritional and metabolic perturbations), but a pathogen among the group of viruses, bacteria, myxozoa, microporidia, ciliata, trematoda or turbellaria is generally involved. Their presence reflects an unbalanced palaeoenvironment in the basin where the fishes of the “Pesciara di Bolca” fossilized.