Strategic investment models, though popular in the theoretical literature, have rarely been tested empirically. This paper develops a model of strategic investment in inpatient procedure markets, which are well-suited to empirical tests of this behavior. Potential entrants are easy to identify in such markets, enabling the researcher to accurately estimate the entry threat faced by different incumbents. I derive straightforward empirical tests of entry deterrence from a model of patient demand, procedure quality, and differentiated product competition. Using hospital data on electrophysiological studies, an invasive cardiac procedure, I find evidence of entry-deterring investment. These findings suggest that competitive motivations play a role in treatment decisions.