Data from field experiments are used to estimate the yield benefit of corn hybrids containing event MON 863 relative to nontransgenic corn hybrids without corn rootworm control and with a soil insecticide for corn rootworm control. Over typical ranges for corn rootworm population pressure, event MON 863 provides a yield benefit of 9-28% relative to no control and of 1.5-4.5% relative to control with a soil insecticide. For a reasonable range of prices and yields, the value of the event MON 863 yield benefit is $25-$75/ac relative to no control and $4-$12/ac relative to control with a soil insecticide, depending on corn rootworm pressure. Because of the low correlation between yield loss and the root rating difference, a common empirical finding when estimating yield loss with root ratings, the 95% confidence intervals around these averages are quite wide. Though on average, event MON 863 has substantial value, the wide confidence intervals imply that farmers will see a wide variety of actual performance levels in their fields. This uncertainty in the realized yield benefit is not due to any property of event MON 863, but rather due to the inherent randomness in the numerous environmental and agronomic factors determining a corn plant's yield and yield response to corn rootworm larval feeding damage.