Measurements of ten characters were made on each of 156 specimens of Apodemus sylvaticus (L.) from eight islands in the Inner and Outer Hebrides and from two localities on the adjacent mainland of north-west Scotland. The characters were occipito-nasal length, weight, tail length, hind foot length, pectoral stripe length, tooth row length, values, chroma, incisor width and tooth wear. Tooth wear is a measure of age and a regression adjustment was used to bring all characters to a uniform age class. The pectoral stripe measurement was analysed using a logarithmic transformation. An analysis into canonical variates was made, the object being to account for the largest possible part of the variation between groups using a limited number of linear combinations of the original measurements. Most of the variance was contained in the first two canonical variates and from the dispersion of the means of the samples it appeared that the populations of Apodemus separated into two main groups. The first contained animals from Raasay, Applecross, Laga, Mull and Lewis and the second those from Barra, South Uist and North Uist. The Rhum and Colonsay mice were to some extent distinct from both groups and from each other, with the former the more isolated. The analysis confirms that differences between all the populations examined are small and that no distinct island species is readily recognizable. It appears that evolution has taken place on each island independently with no evidence of the island populations having been derived from one basic stock. It is proposed that the specific name hebridensis should be dropped, that A. sylvaticus hamiltoni (Hinton) be recognized as a large form from Rhum and that the remainder from the localities investigated should be referred to as A. sylvaticus sylvaticus (L).