The objective of this study is to measure the concentration levels in the auditing business market in Colombia for the period 2010-2018, using the concentration index methodology allowing us to know the number and share of audit firms that make up the market, using the Hirschman-Herfindahl index, the n-firm concentration ratio, and Adelman’s number’s-equivalent index. Results indicate that the audit market for companies listed on the Colombian stock market is highly concentrated on the Big Four, preventing small firms from entering that market.