This paper looks at the impact of patient knowledge on utilization and quality in physician services markets, developing a theoretical framework based on an alternative to the “market failure” perspective first proposed by Arrow (1963). Specifically, this paper looks at how outcomes in physician services markets are determined by whether patient and physician knowledge are substitutes or complements in health production. Empirical testing of the theoretical predictions indicates patient and physician knowledge have changed from substitutes to complements in recent years, and that this change may be hindering a more consumer-driven market from ensuring high quality outcomes.