The European flat oyster, Ostrea edulis L, represents an important economically oysterproduction in Southern Italy, widespread in natural beds along the coast. The practice to beeaten raw is an everlasting concern for possible health risk, needing stringently to monitorthe health of aquatic environment. A screening survey, for hystopathological examination,was undertaken by harvesting O. edulis from different sites along the Apulian coast:Manfredonia, Margherita di Savoia, Monopoli, Taranto and Tricase. Tissue samples ofdigestive gland, kidney, gonad and gill were provided for morphologic study in LightMicroscopy (LM), Transmission Electron Microscopy (TEM) and Scanning ElectronMicroscopy (SEM) analysis. LM observations revealed spherical cytoplasmic inclusions,as basophilic prokaryote colonies in about 5% of oysters. TEM and SEM confirmed thepresence of intracytoplasmic inclusions of Rickettsia-like organisms (RLOs), merely in theepithelial cells of digestive gland tubule tissues of 13 adults. Within intracytoplasmicvacuoles, RLOs exhibited a prokaryotic characteristic ultrastructure with transverse binaryfission, a DNA zone full of chromatin fibers and a granular periplasmic ribosome zone. O.edulis were found positive for RLOs in wild oysters from Manfredonia, while the othersites were found free of pathological inclusions. We present the first report of a Rickettsialikeinfection in the Apulian wild oyster O. edulis from Italy, including an ultrastructuraldescription and pathological characterization.