The seasonal dynamics of 8 parasite taxa in zebra mussels Dreissena polymorpha were studied in the Meuse River (NE France) over a 3 yr period. In total, 69.5% of sampled organisms were infected. Among observed parasite species, Ophryoglena spp. and to a lesser extent Rickettsiales-like organisms (RLOs) displayed seasonal dynamics, with lower prevalence during warmer months negatively correlated with gonadal development in the host, water temperature and phytoplankton concentration. Furthermore, this study highlights a positive correlation be tween the prevalence rates of Ophryoglena spp. and RLOs. No temporal variations were ob served for the ciliates Sphenophrya dreissenae and Conchophthirus acuminatus. Concerning trematode infection, no defined seasonal pattern was observed. Thus, for more reliability in future biomonitoring studies involving zebra mussels, it will be important to include the influence of parasites and their temporal dynamics.