Central American spiny rats (Proechimys semispinosus) maintained in outdoor enclosures were fed fruits from 97 species of native and naturalized forest plants to examine patterns of fruit and seed exploitation. Individuals had very broad diets and consumed soft parts or seeds of all but three species of fruits included in the trials. Fruits and seeds were eaten even though individuals were provided with abundant alternative food. For most species of fruits that contained a fleshy aril or mesocarp spiny rats generally consumed both seeds and fleshy parts. Spiny rats often exploited seeds with hard endocarps even when those seeds were surrounded by an abundant pulpy mesocarp or aril that was also eaten. Spiny rats also preferentially ate seeds of several large-seeded species and primarily peeled off the mesocarp or aril. Seeds of species that contained no mesocarp or aril were also quickly eaten. Fruits from trees in the Moraceae were consumed entirely including the seeds. Results indicate that because of their abundance and broad frugivorous-granivorous diets P. semispinosus are important seed predators in tropical forests within their range. If these rodents scatterhoard seeds as has been found for another species in the genus then they may also function as important but overlooked seed dispersers of many tropical forest plants.