The retail clinic is an innovation that has the potential to improve competition in health care markets. Given concern about inefficient use of the emergency room (ER) increasing health care costs, we use all ER visits in New Jersey from 2006-2014 to examine the impact of retail clinics on ER usage. We find that people residing close to an open clinic are 4.1-12.3 percent less likely to use an ER for preventable conditions and for minor acute conditions. Our estimates suggest annual cost savings of over $70 million from reduced ER usage if retail clinics were readily available across New Jersey.