GAAS = PCAOB Standard No. 1

PCAOB Auditing Standard No. 1 requires that auditors' reports on audits and other engagements relating to public companies and other issuers include a reference that the engagement was performed in accordance with the standards of the PCAOB. This replaces the previous reference to generally accepted auditing standards, or GAAS.  However, according to the SEC's Order on May 15, 2004,  

The PCAOB adopted those generally accepted auditing standards, including their respective effective dates, as they existed on April 16, 2003, as interim PCAOB standards. Therefore, changing the reference from "generally accepted auditing standards" to "the standards of the Public Company Accounting Oversight Board (United States)" does not change the substantive procedures performed by an auditor. Because GAAS and the standards of the PCAOB are one and the same for PCAOB-registered public accounting firms, the PCAOB believes that a reference to GAAS in auditors' reports would no longer be appropriate or necessary.