Eighty percent of all peripheral facial nerve paralysis is idiopathic in origin(Bells palsy); specific etiology can be demonstrated in the remaining 20 percent. Current researchs suggest that Bell's palsy may be an autoimmune-postviral disease or may be caused by reactivation of latent Herpes Simplex virus infection. During the hospitalization of cancer patients, there are many factors which suppress the host resistance and favor the viral infection or reactivation. In cancer patients, peripheral facial nerve paralysis can be caused not only by viral infection or reactivation but also by cancer extension or complications of antineoplastic agents. Differentiation of these possible etiologies ia important in planning further tberapy. The authors experienced 3 cases of acute peripheral facial nerve paralysis occured in cancer patients; the first occured after viral prodrome of fever and herpetic penile skin lesion in 56-year-old man who was suffered from the acute blastic crisis of chronic myelogenous leukemia, the second occured in 16-year-old boy who was suffered from lymphosarcoma cell leukemia with meningeal and bone marrow involvements, and the third was seen in 39-year-old man with small cell carcinoma of the lung which was chemosensitive but recurred frequently. Although the exact cause of facial palsy in these patients could not be determined, the clinical picture suggests facial paralysis caused by viral etiology rather than tumor extension or complications of antineoplastic agents. In order to decermine the exact etiology, additional tests such as virologic studies, polytomography of the temporal bone and cranial CT scan are indicated.