We report on a survey of the small mammal communities of Anaho Island and the mainland surrounding Pyramid Lake in the Great Basin of western Nevada. Ten rodent species were detected on the mainland, but only the deer mouse (Peromyscus maniculatus) was detected on Anaho Island. Although the mean abundance of deer mice on the Pyramid Lake mainland was more than double that of Anaho Island (12.5 ± 10.1 individuals per trap grid compared with 5.0 ± 3.4 individuals per trap grid), we did not detect a significant difference between locations. Deer mice on Anaho Island were significantly larger in body size (mean body length = 86 ± 4 mm) than mainland mice (mean = 75 ± 7 mm), but it is unclear what mechanisms might have produced the observed divergence in body size.