This study describes patterns of geographic variation in morphometric characters of the green toad, Bufo viridis, in the western part of its distribution, including the Italian Peninsula and the islands of Sardinia and Corsica. The causes of this variation were investigated by comparing observed patterns of interpopulational differences to hypothesized factors derived from climatic and geographic variables, through the use of canonical correlation analysis and partial Mantel tests. Among-population differences in morphometric characters include both size and shape. Island populations were found to have larger body sizes than mainland populations, and there was an association between climatic factors and morphological characters. Partial Mantel tests carried out on a number of possible causal hypotheses, both climatic and geographic, suggest that a large portion of this association should be interpreted as a spurious effect of genetic isolation between island and mainland populations and of the limiting effect of geographic distance in determining gene flow.