Bt-corn, a genetically engineered insect resistant variety, has been adopted by almost one-quarter of all corn farmers, resulting in economic impacts on both conventional corn growers and Bt-corn growers. we estimate changes in profits for both types of farmers with different levels of seed premiums, yield increases and adoption rates. We find that Bt-corn growers will see their profits decline when the adoption rate and seed premium are high, if they are not offset by higher yields. Conventional corn growers will always experience a decline in profits because the yield increase from Bt-corn causes corn price to fall.