Abstract Spatial, temporal, intraspecies and interspecies variation of selenium concentration in five species of intertidal molluscs from Jervis Bay, Australia was investigated. The selenium concentrations measured in molluscs were lower than in those reported from overseas studies. The selenium concentrations did not differ from those reported for other relatively unpolluted Australian marine environments. Nerita atramentosa had the lowest selenium concentration, followed by A. constricta and B. nanum, then O. angasi, with M. marginalba having the highest concentrations of selenium. Species differences in selenium concentration were also reflected in total body burdens of selenium. The differences in selenium concentration among species varied temporally, with the magnitude of the differences varying among months. The population distributions of selenium concentration generally exhibited positive skewness, with most individuals within each species containing low concentrations of selenium. Only a few individuals exhibited high concentrations of selenium, extending the right tail of the frequency distribution. Skewness could not be explained by mass and size differences and is probably the result of micro-habitat differences. Selenium concentrations did not have any consistent relationship with mass or length of the species. The trend was towards lower selenium concentrations as mass of the mollusc increased. This means that mass or length cannot be used as an index of selenium concentrations in populations of the species examined in this study. Significant variation in selenium concentration existed on all spatial scales (location, site) for all species with the exception of the bivalve O. angasi. For the gastropods, the order of sites from lowest to highest selenium concentration differs among sampling times, with no predominance of one site over another. All species showed significant temporal variation in selenium concentration and selenium body burdens but there were no consistent trends over time, or consistent relationships with body mass. At most sites the lowest selenium concentrations and selenium body burdens were recorded in January and associated with high body tissue mass in O. angasi, and spawning in N. atramentosa, B. Nanum and M. marginalba.