This article investigates the relationship between supplier concentration and competition in the market for audit services. The study is motivated by the concern that high levels of concentration may be detrimental, resulting in lower levels of competition, which could harm clients through higher fees and lower levels of service. However, a counterargument is that high levels of concentration may not be detrimental but may result because market leaders display exceptional performance, providing lower‐priced audits (perhaps due to economies of scale) and/or enhanced service to clients. We obtained audit fee and financial data on 140 life and health insurance companies and 101 property and casualty insurance companies. Our findings indicate that concentration is negatively associated with fees, suggesting that higher levels of concentration are related to higher levels of price competition (i.e., lower fees). Additionally, we address the validity of concentration as a surrogate for competition by examining competition among the market leaders. Our analysis examines the fees paid by 47 insurance companies that switched auditors during the sample period. We investigate the effect of industry specialization on fees paid by clients that switch auditors, finding evidence of significant fee cutting among market leaders for each others' clients but no evidence of fee reductions for clients switching from nonleaders to market leaders. This is consistent with the claim that there is significant price competition for clients among the market leaders, suggesting that high concentration need not result in low levels of price competition (i.e., higher fees).