Hermit crabs depend on gastropod shells that influence many characteristics of their life histories. The relationship between shell utilization patterns and biological attributes enables comparisons among populations and discussions of the influence of the environment (shell supply) on hermit crab biology. This study was undertaken in a cobble/boulder low slope rocky shore in Grande Beach, São Sebastião, São Paulo State, Brazil. Crabs were randomly sampled, measured (shield length), and their sexes were determined. Shells were identified, sized (height, width, and aperture length), and weighed. Four hermit crab species were registered: Clibanarius antillensis, Paguristes tortugae, Pagurus criniticornis, and Calcinus tibicen. Shell use was influenced by shell availability, despite the selection of certain shell types and sizes by hermit crabs. Shells were not considered a limiting resource to this hermit crab assemblage, and shell availability was dependent on shell type and size as well as on individual size and species composition of the hermit crab assemblage (presence of competing species). Shell partitioning among crab species was recorded and associated with species coexistence in this area. Differential shell use was recorded among size and reproductive classes of C. antillensis. There was a tendency toward high numbers of ovigerous females in relatively lighter (smaller) and small-aperture shells, such as Cerithium atratum and Morula nodulosa, which was associated with growth restriction and low fecundity imposed by shell morphology.