Temporal patterns in metazoan parasite community diversity of Crassostrea gigas, (Lamellibranchia: Ostreidae) were studied in the Exe Estuary at monthly intervals over one year and in relation to host age-classes. A total of four metazoan species was found to parasitize C. gigas in the Exe Estuary: the turbellarian Paravortex sp., cercaria Lepocreadiidae, metacercariae of Renicola roscovita and the copepod Mytilicola intestinalis. Only R. roscovita and M. intestinalis were present in all months throughout the year and in all host age-classes. Analysis of the metazoan parasite community at individual host level revealed little variation in community structure with respect to season or host age, as only a slight increase in diversity values was observed during the summer months. However, community diversity does vary from year to year, as shown by comparison between host age group samples in three consecutive years. None of the parasites are specialist to oysters but all appear to be widespread and abundant parasite of other lamellibranch species.