Gene flow can be expected to occur in many crop/weed complexes if the crop and the weed have sympatric ranges, are sexually compatible, have flowering times that overlap, and share a common pollinator. These conditions are met in a large number of crop/weed complexes; however, the consequences of gene exchange between crops and wild relatives on a wide scale, and the potential fate of escaped engineered genes, remain generally unknown. It is believed that an examination of the fitness of weed/crop hybrids will provide insight into the potential fate of genetically engineered genes, or transgenes, in the wild. We examined several fitness correlates of weed X crop hybrids between crop sorghum and a related noxious weed, johnsongrass. Comparisons were made with nonhybrid johnsongrass under agricultural conditions. Hybrid weeds did not show any significant increase or decrease in time to flowering, panicle production, seed production, pollen viability, tiller production, or biomass. We conclude that a transgene that is either neutral or beneficial to johnsongrass would likely persist in populations growing in agricultural conditions under continued gene flow from the crop.