Background: Herpetic disorders cause pain and skin lesion. So, asymmetric temperature of both sides of the involving dermatome has been reported in thermogram. This study examined the usefulness of infrared thermography for a predictor of post-herpetic neuralgia (PHN). Methods: Patients with acute herpes zoster who underwent nerve block were randomly selected. Biographic data, including age, gender and times of onset of the skin lesions, development of PHN, combined diseases were recorded. Infrared thermography was performed and subjective pain severity, dysesthesia and allodynia, skin lesion size were assessed. Results: The temperature differences between the lesion site and the contralateral site at lateral and posterior were significantly correlated with lesion size (P