Ground beetles (Coleoptera: Carabidae) were sampled in conventional and genetically modified herbicide-tolerant (GMHT) corn, Zea mays L. (Poaceae), planted under rotation with canola, Brassica L. (Brassicaceae), or continuously cropped corn to investigate the influence of corn variety and rotation on the structure of carabid assemblages. Corn variety, cultivation regime, and their interaction all influenced overall carabid activity density. Weed management associated with corn variety influenced the activity density of a few carabid species and this was attributed to changes in vegetation. Some smaller bodied carabids such as Bembidion quadrimaculatum L. were less abundant in GMHT plots, probably because weed density was higher in midseason, but the opposite was observed for larger bodied carabids such as Pterostichus melanarius (Illiger). Overall, rotating corn with canola had a stronger effect on carabid community structure than did corn variety. We suggest that GMHT corn has little impact on the overall carabid fauna but may influence the activity of certain species through effects on the weed community.