Abstract: Empirically, a higher frequency of lightning strikes is associated with slower growth in labor productivity across the 48 contiguous U.S. states after 1990; before 1990, there is no correlation between growth and lightning. Other climate variables (e.g., temperature, rainfall, and tornadoes) do not conform to this pattern. A viable explanation is that lightning influences IT diffusion. By causing voltage spikes and dips, a higher frequency of ground strikes leads to damaged digital equipment and thus higher IT user costs. Accordingly, the flash density (strikes per square kilometer per year) should adversely affect the speed of IT diffusion. We find that lightning indeed seems to have slowed IT diffusion, conditional on standard controls. Hence, an increasing macroeconomic sensitivity to lightning may be due to the increasing importance of digital technologies for the growth process. {\copyright} 2012 The President and Fellows of Harvard College and the Massachusetts Institute of Technology.