The habitat-related microgeographical body size variations in red foxes Vulpes vulpes living in two separated areas of Mediterranean Spain, the Central Ebro Valley (CEV) and Doáana National Park (DNP) are analysed. In both areas, samples taken from good and bad fox-habitats were compared regarding body weight and head and body length. In the Ebro Valley, foxes collected in the good habitat were heavier (14%, P < 0.001 for males; 9%, P < 0.01 for females) and larger (4%, P < 0.01 for males; 1%, P < 0.05 for females) than those collected in the bad habitat. In Doáana, males from the good habitat were 19% heavier (P < 0.01) and 3% longer (P < 0.05) than those from the poorer one. The average weight and size of DNP vixens did not show significant differences, although both are higher in the good habitat. It is shown that body size of adult foxes can vary, linked to habitat change even across short geographic distances. Some tentative explanations for these results are discussed.