Pre-college student participation in science fairs, robotics competitions, computing contests and other science, technology, engineering, and mathematics (STEM) competitions increases every year in the United States. This is despite the fact that little is known about the relationship between STEM competition participation and career interest in STEM. Through logistic regressions, this study addresses three main research questions: Controlling for student background variables and prior STEM career interest, does participating in a STEM competition increase the likelihood of STEM career interest at the end of high school? Does the field of competition (robotics, engineering, science fair, information technology) a student participates in influence the sub-discipline of STEM career interest? And, what is the relationship between the number of competitions participated in and the probability of interest in a STEM career? The study uses data from the 'Outreach Programs and Science Career Intentions' survey (N = 15,847), a large-scale sample of university students enrolled in mandatory English courses. Our data reveal three results of interest. First, students who participate in STEM competitions are more likely to express interest in a STEM-related career at the end of high school than are students who do not participate, even when students' prior career interest in STEM is controlled for. Second, the relationship between competition participation and interest in a STEM career appears to be domain specific. Third, the impact of competition participation on pursuit of a STEM career is three times stronger when students compete in more than one competition. These findings suggest that competitions are an effective way to foster career interest in specific STEM careers.