Aflatoxin is a potent toxin produced by the fungus Aspergillus flavus.  Contamination of corn, Zea mays L., with aflatoxin greatly reduces the value of corn grain and is a major impediment to profitable corn production in the South.  Infestation of developing corn ears with southwestern corn borer, Diatraea grandiosella Dyar (Lepidopera: Crambidae), increases the likelihood of aflatoxin contamination.  In this investigation, six corn hybrids with different levels of resistance to southwestern corn borer damage and aflatoxin contamination were evaluated for damage by southwestern corn borer and aflatoxin contamination after infestation with southwestern corn borer at 7-d intervals from 35?84 d after planting and inoculation with an A. flavus conidial suspension.  Transgenic (Bt) hybrids exhibited excellent resistance to southwestern corn borer and less aflatoxin contamination than conventional versions of the same hybrids.  A conventional hybrid with intermediate resistance to southwestern corn borer also exhibited relatively low levels of aflatoxin contamination.  A conventional hybrid selected for resistance to aflatoxin contamination was heavily damaged by southwestern corn borer, but exhibited little aflatoxin contamination.  Hybrids that have resistance to both southwestern corn borer and aflatoxin contamination appear to have the greatest potential for effectively reducing losses to aflatoxin in the South.  Damage by southwestern corn borer to plants in both the vegetative and reproductive stages of growth can increase aflatoxin contamination in susceptible corn hybrids.