The distribution patterns exhibited by some larval decapod crustaceans within the York River system and adjacent lower Chesapeake Bay, Virginia, suggest means by which young stages can be recruited to the adult benthic and bentho-pelagic populations. Species considered are four caridean shrimp ( Crangon septemspinosa, Hippolyte pleuracantha, Ogyrides limicola and Palaemonetes spp.) and 12 brachyuran crabs ( Callinectes sapidus, Cancer irroratus, Hexapanopeus angustifrons, Neopanope sayi, Ovalipes ocellatus, Pinnixa chaetopterana, Pinnixa sayana, Pinnotheres maculatus, Pinnotheres ostreum, Rhithropanopeus harrisii, Sesarma reticulatum and Uca spp.). Larvae of the species which are heavily dependent on estuarine habitats were more abundant in the lower layer of the water column where net transport is upstream than near the surface and thus tended to be retained within the estuary. For these species, retention of larvae in the estuary may be the primary mechanism of recruitment to estuarine adult populations. No distributional adaptations for retention within the bay were apparent among larvae of Cancer irroratus, Crangon septemspinosa and O. ocellatus, species not restricted to estuarine habitats, nor for Callinectes sapidus, a migratory estuarine species which also occurs on the inner continental shelf. While chance retention of larvae may affect recruitment, especially of C. septemspinosa, the major mechanism by which the bay populations of these species are restocked is probably the immigration of juveniles or adults from inner shelf waters. Thus, there appear to be two basic mechanisms of recruitment of young to estuarine decapod crustacean populations: (1) recruitment by retention of larvae and (2) recruitment by immigration of juveniles and adults. Various combinations of the two mechanisms are expressed among the different populations of an estuary, and the tendency of a species to exhibit one more than the other is influenced primarily by the degree of its dependence upon the estuary.