Field studies were conducted near College Station, TX, in 2006 and 2007 to evaluate the economic impact of common sunflower interference in field corn. A density of one common sunflower per 6 m of crop row caused a yield loss of 293 kg ha1. Estimated losses at a net corn price of $0.08 kg1was $92 ha1for infestation levels of four common sunflower plants per 6 m of row. Corn yield was increased by 32 kg ha1by each 1,000 plant ha1increase in corn planting density. Corn planting densities of 49,400 and 59,300 plants ha1provided the greatest net returns with or without the presence of common sunflower competition. Corn yields were reduced by extended duration of sunflower competition, with losses exceeding 1,500 kg ha1per week and increasing in magnitude at a decreasing rate throughout the growing season. Herbicide treatments provided net returns of $600 to $1,300 ha1above no weed control in both 2006 and 2007. Net returns of $609 and $653 ha1were obtained without the use of any herbicide for sunflower control. Determining the economic impact of common sunflower interference in field corn allows producers to estimate the overall net return on the basis of duration of common sunflower interference and density, while considering varying net corn prices, crop planting density, and herbicide application costs.