Regulators have expressed concerns that auditors become less effective external monitors as the length of the auditor-client relationship increases. I examine how audit firm tenure is associated with changes in financial reporting quality due to mandatory adoption of International Financial Reporting Standards. I argue that auditors were integral in proper implementation of IFRS and could have mitigated potential negative consequences associated with IFRS adoption. My findings suggest that short audit firm tenure was associated with a decrease in quality, relative to those with medium length tenure. Differences between clients with medium and long tenure are generally not significant. Other results indicate that companies with a Big 4 auditor had greater improvements, or smaller decreases, in reporting quality relative to non-Big 4 clients. My results do not support concerns that longer tenure impairs audit quality. My study is also relevant to standard setters as they evaluate the results of IFRS adoption.