The diagnosis of pre-eruptive varicella cerebellitis is usually based on a history of exposure and thus depends on a subjective clinical assessment. The confirmation of the diagnosis has traditionally depended on the development of skin manifestations of varicella and on varicella-zoster antibody seroconversion. Confirming the diagnosis of pre-eruptive cerebellar ataxia or encephalitis early in the course of a viral infection may save the patient unnecessary tests, procedures, or attempts at therapeutic intervention. A patient is reported in whom, after clinically suspecting a diagnosis of pre-eruptive varicella cerebellitis, the diagnosis was confirmed by performing polymerase chain reaction analysis of varicella-zoster virus DNA in peripheral blood leukocytes and cerebrospinal fluid. The patient developed skin manifestations of varicella 5 days after the onset of neurologic symptoms and 15 days after known exposure. In some patients with preeruptive varicella cerebellitis, polymerase chain reaction may be extremely useful for rapid confirmation of the diagnosis.