Securities regulators around the world are considering the costs and benefits of alternative policies for providing information to financial markets on corporate internal control. These policy options differ on the level of auditor involvement, among other dimensions. We examine the association of relative auditor involvement and auditor characteristics with Section 302 internal control disclosures made by US ‘non-accelerated filers’ from 2003 to 2005. We find more material weaknesses disclosed in the fourth quarter, when there is relatively more auditor involvement, relative to the first three quarters. Clients of larger audit firms have higher disclosure rates (although they are probably less risky due to more stringent client acceptance standards), but this difference is due to fourth quarter disclosures. Audit firms with Section 404 experience also have greater material weakness disclosure, implying process improvement associated with knowledge sharing across engagements. Collectively, our results shed light on ways to increase the effectiveness of internal control regulation.