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Morphological variation was studied among 209 pouched mice (Saccostomus campestris, Peters, 1846) from 104 localities in the southem African subregion. Climatic variables for these localities were generated using a climatic surface model developed with data from existing meteorological stations. These estimates of temperature, rainfall and seasonal variability were strongly correlated with latitude, so that the different climatic factors covaried. Extemal measurements (body, tail and ear length) and body mass were strongly correlated with condylo-basal skull length which was taken as a more reliable measure of body size. Geographical variation in body size was significantly correlated with latitude, temperature and seasonality although these correlations appeared to be largely the result of a positive relationship between size and rainfall. In contrast, temperature apparently had little effect on morphology as there were no clear correlations between temperature and the size of appendages (tail or ear length). Rainfall might be more important than ambient temperature as a factor influencing body size in small fossorial and semi-fossorial mammals which spend most of their lives in warm subteffanean microhabitats. Meanwhile, the smaller body size of pouched mice from localities with lower rainfall may represent an adaptation to reduce total energy requirements in arid and semi-arid areas where primary production and food availability is low.