The article advances a prospective case study design in social sciences as an alternative to traditional post hoc case study research in deductive theory testing. It is argued that some limitations of post hoc qualitative methods in deductive theory testing can be alleviated by using a prospective case study design, where researchers formulate a set of theory-based hypotheses in respect to the evolution of an ongoing social process and then test these hypotheses at a predetermined follow-up time in the future by comparing them with the observed outcomes using pattern matching or a similar technique. Some challenges of conducting prospective research in social sciences are discussed. An illustration of the application of this method in deductive testing of two competing theories is provided.