We analyzed grain yield data from annual field experiments during 1990-2010 in Wisconsin to test hypotheses that maize expressing these transgenic traits alone or in combination (stacked) has greater productivity (as measured by the mean harvested yield) and lower production risk (as measured by the variance, skewness and kurtosis of harvested yield). Compared with conventional hybrids, the impact of transgenic traits (both single and stacked traits) on mean yield ranges from -12.2 to +6.5 bushels per acre. This shows that reducing yield risk is an important source of benefits of transgenic technology, especially for stacked traits.Correspondence