The number of small audit firms serving public companies shrank dramatically during our sample period of 2003-2018. Sixty percent of triennially inspected U.S. audit firms that registered with the PCAOB in that era subsequently de-registered. This study examines the strategic decisions of small U.S.-based audit firms to exit or remain in the PCAOB-regulated audit market. Prior research shows that many small firms exited in the early post-SOX period when major PCAOB regulations were initiated. However, we find that most de-registrations in our broader sample period do not occur in years proximate to such regulatory shocks, including the previously unstudied initiations of Form 2, 3, and AP disclosures. We propose that de-registrations largely are due to strategic costs and benefits other than PCAOB initiatives. We find that proxies for these strategic constructs are significant explanators of decisions to de-register. We investigate the previously unstudied topic of what happens to small audit firms after they de-register. We find that more than half continue to operate as independent entities; to provide audit and attest services; and to have their audits peer reviewed. Therefore, they provide audit services to the large market of non-public companies. The approximately twenty-five percent of firms that merge surrounding de-registrations are larger than other de-registering firms, charge higher fees, and have higher audit quality.