European corn borer (ECB) tunnel length was measured in on-farm strip trials for ten years between 1995-2004 in 3,031 U.S. Midwest locations and related to the difference in corn yield between Bt corn hybrids and their closely related non-Bt relatives. The purpose of this research is to provide geographically-referenced information characterizing ECB infestation and its effect on corn yield to support the development of accurate production risk management strategies. Across years and states, average ECB infestation ratings ranged from 1 to 8 (representing non-Bt yield losses between 0 and 12 bu/A) and averaged 3.3 (4-5 cm of tunneling/plant; yield loss of 5.3 bu/A). Considering corn grain valued at $2.40/bushel and $21/unit for Bt corn seed, the financial breakeven rating was 2.4. Averages tell part of the story, however, as substantial differences exist among geographic locations and years for ECB infestation frequency and severity. The probability of ECB yield loss from a non-Bt hybrid to exceed the investment in Bt corn seed is dependent upon geography, from 60% in Michigan, to 78% in Indiana and 89% in Iowa, Minnesota, and Nebraska. Moderate to severe ECB infestations (rating >3.8) occurred at significant frequencies in Michigan (20%) and Indiana (33%) as Iowa (40%), Minnesota (44%), and Illinois (50%). Although geographic differences are most important, differences did exist among years for ECB infestation severity. Five of the ten test years produced ratings between three and four, with two years higher at 4.3 (1996, 1997) and three lower at 2.5 (1995, 1998, 2004). While Bt corn use rates have increased, a trend for suppression of ECB infestation is not obvious. In consideration of ECB infestation frequency and severity in most geographic areas, consideration of Bt corn use should be encouraged as a valuable tool in the risk management strategy of a corn production system.