BACKGROUND Although Bell's palsy (BP) is the most common cause of peripheral facial palsy (PFP), other etiologies merit investigation. CASE REPORT A 60-year-old female patient presented with recurrent bilateral PFP. Although the patient had a history of acute myeloid leukemia (AML), she had initially been diagnosed with BP-related PFP and had been treated accordingly. When the PFP recurred, additional diagnostic tests were performed. The resulting immunohistochemical profile included CD3 positivity in a few reactive T lymphocytes; positivity for myeloperoxidase in atypical cells; and focal positivity for CD34 and proto-oncogene c-kit proteins in neoplastic cells, thus confirming the suspicion of mastoid infiltration caused by relapsed AML. CONCLUSION In patients with neoplastic disease, a finding of PFP calls for extensive investigation in order to rule out the involvement of the temporal bone.