Patents and trade secrets are often considered economic substitutes. Under this view, inventors can decide either to maintain an invention as a trade secret or to seek a patent and disclose to the public the details of the invention. However, a handful of scholars have recognized that because the patent disclosure requirements are not always rigorous, inventors may sometimes be able to keep certain aspects of an invention secret, yet still receive a patent to the invention as a whole. Here, we provide further insight into how trade secrets and patents may act as complements. Specifically, we introduce the concept of “data-generating patents,” which refer to patents on inventions involving technologies that by design generate valuable data through their operation or use. For instance, genetic tests and medical devices produce data about patients. Internet search engines and social networking websites generate data about the interests of consumers. When data-generating inventions are patented, and the patentee enjoys market power over the invention, by implication, the patentee also effectively enjoys market power over the data generated by the invention. Trade secret law further protects the patentee’s market power over the data, even where that data is in a market distinct from the patented invention and especially after the patent expires or is invalidated. We contend that the use of patents and trade secrets as complements in this manner may sometimes yield socially harmful results. We identify the conditions under which such results occur and make several recommendations to mitigate their effects.