Repeated measurements of captive-born Gaboon vipers Bitis gabonica from an inbred stock examined the degree to which an animal's size and shape are affected by food intake. We also used the level of asymmetry in dorsal coloration as an index for possible genetic (inbreeding?) effects. Both of these factors, and the interaction between them, affected phenotypes of the young snakes. Snakes raised with abundant food differed from their less well-fed siblings not only in size, but also in body mass relative to snout–vent length, head length relative to snout–vent length, head width relative to head length, and fang length relative to jaw length. Hence, our data show that body proportions (including the feeding apparatus) can be influenced by the environment after birth.