A previously healthy 55-year-old woman developed abnormal sensation on the right occipital region. It expanded for the following three weeks. On admission, examination revealed abnormal and decreased sensation in touch and pinprick at right C2 to C6 dermatome without skin lesion. There was no muscle weakness. Deep tendon reflexes were more active in the right than in the left. MRI demonstrated a lesion of isointensity on T1-weighted, hyperintensity on T2-weighted, which was enhanced with contrast material on gadolinium-enhanced T1-weighted image at the upper cervical spinal cord corresponding to C2. Laboratory studies showed no immunosuppression and autoantibodies. The antibody index to varicella-zoster virus (VZV) was elevated in the cerebrospinal fluid (CSF). This finding prompted us to a diagnosis of myelitis of zoster sine herpete. VZV is thought to be a causative agent in cases of CNS infections of unknown etiology such as myelitis, even in the absence of skin manifestations. Amplification of VZV DNA by PCR in the CSF and the detection of an intrathecal production of anti-VZV antibodies have important diagnostic value, although their presence depends on the timing of the CSF sampling. The percentage of PCR-positive cases drops after seven or ten days, whereas that of specific antibodies-positive cases elevates. Because VZV myelitis are usually protracted, PCR does not always provide an exquisite sensitivity. Thus, the evaluation of antibody index provides the evidence of intrathecal production of anti-VZV antibodies. That is expressed as CSF antibody titer/serum antibody titer/CSF IgG/serum IgG. This quotient superior to 1.5 or 2.0 suggests CNS synthesis. As the sample of our patient was taken relatively late, this value was diagnostic. We would like to emphasize the importance of making precise diagnosis and adequate initial treatment in patients with myelitis of unknown etiology even if there is no skin lesions.