Based on the premise that the quality of the audit is related to the quality of the financial reporting, the purpose of this chapter is to verify if the audit is a determining factor in derivative financial instruments disclosures. However, the academic literature has revealed that audit quality is influenced by a number of factors, such as gender, experience, and auditor's fees, as well as the type of audit firm (Big4 or not Big4). In order to achieve the proposed objective, a disclosure index was prepared, based on the requirements of the International Accounting Standards Board (IASB), applied to companies listed on Euronext Lisbon, excluding the sports corporations. The results revealed that the level of disclosure is influenced by the size of the audited company and by the auditor's gender, being greater in the larger companies and in the companies audited by a male auditor.