Patterns of size variation in insular mammals have been used to support the claim that mammals have a single optimal body size. This hypothesis enjoys wide support, despite having been questioned on both theoretical and empirical grounds. It is claimed that species of optimal size maintain the highest population densities. Therefore these species are thought to inhabit the smallest islands, where larger and smaller species are generally absent. We sought such a pattern by testing how area affects the body sizes of the largest and smallest carnivore species on islands. Using data on carnivores from 322 islands, we found that the sizes of carnivores on small islands tend to be close to the order's mode. Furthermore, we found that the size distribution of carnivore species that inhabit islands resembles that of those whose range is entirely continental. We conclude that insular carnivores provide no support for theories proposing a single optimal size, and we suspect such theories are also flawed on theoretical grounds.