This paper focuses on a sample of 261 companies that disclosed at least one material weakness in internal control in their SEC filings after the effective date of the Sarbanes‐Oxley Act of 2002. Based on the descriptive material weakness disclosures provided by management, we find that poor internal control is usually related to an insufficient commitment of resources for accounting controls. Material weaknesses in internal control tend to be related to deficient revenue‐recognition policies, lack of segregation of duties, deficiencies in the period‐end reporting process and accounting policies, and inappropriate account reconciliation. The most common account‐specific material weaknesses occur in the current accrual accounts, such as the accounts receivable and inventory accounts. Material weakness disclosures by management also frequently describe internal control problems in complex accounts, such as the derivative and income tax accounts. In our statistical analysis, we find that disclosing a material weakness is positively associated with business complexity (e.g., multiple segments and foreign currency), negatively associated with firm size (e.g., market capitalization), and negatively associated with firm profitability (e.g., return on assets).