The study was designed to determine the effects of roads on the diversity, spatial distribution and density of small mammals. Small mammals (5859 individuals) (40 spp.) were snap-trapped in the study. Data resulted from 144,360 trap-nights of effort for an average of 4.06 captures/100 trap-nights. Small mammals community structure and density were both influenced by roads. Community structure in right-of-way (ROW) habitat was different from that in adjacent habitat. The golden mouse, dusky-footed woodrat, brush mouse, pinon mouse and California red-backed vole [Peromyscus boylii, P. truei, Ochrotomys nuttalli, Neotoma fuscipes and Clethrionomys californicus] did not prefer ROW habitat. There were more species present in ROW habitat than in adjacent habitat. Grassland species generally preferred ROW habitat and many less habitat-specific species were distributed in ROW and adjacent habitat. Small mammal density (all species combined) was greater in interstate ROW habitat than in adjacent habitat. This was also true individually for the eastern harvest mouse, white-footed mouse, meadow vole, prairie vole, vagrant shrew, Townsend''s vole and California vole [Sorex vagraus, Reithrodontomys humulis, Peromyscus leucopus, Peromyscus leucopus, Microtus pennsylvanicus, M. californicus, M. townsendii and M. ochrogaster]. Small mammal density was less in county road ROWs than in adjacent habitat, probably because of the small size of these areas. The data indicate that ROW habitat and its accompanying edge are attractive not only to grassland species, but also to many less habitat-specific species that make use of the ROW-edge-adjacent habitat complex. Mortality on interstate highways was greatest for those species with highest density in ROW habitat, and did not appear to be detrimental to populations of these species.