A unifying model of herpes zoster pain presents considerable analytical challenges due to the requirement for prospective data collection and the varying rates of pain resolution reported by individual patients. Demographic, clinical, and quality-of-life measures were collected on 166 human immunodeficiency virus (HIV)-infected patients enrolled in a randomized, controlled trial of antiviral therapy of herpes zoster comparing acyclovir with sorivudine. A 'mixed model' was used to assess factors predictive of pain severity, activity impairment, and sleep interruption. The average rate of change in acute pain was -0.04 unit pain per day for the first month. Chronic pain decreased -0.12 per month for months 1-12. Acute pain severity was positively correlated with number of new skin vesicles, analgesic use, and baseline pain, and negatively related to percentage of lesion healing and crusting. Postherpetic neuralgia was correlated with baseline pain, pain at 1 month, and duration of lesions. Treatment group, gender, race, and CD4 count were not related to change in pain severity. These analyses verify the significance of baseline pain as a significant predictor of pain resolution and average pain severity as a predictor of return to normal daily activities and sleep. The severity of acute pain at presentation and at 1 month are significant predictors of chronic pain.